External Coprocessing

Customize your router's behavior in any language

plan required
This feature is only available with a GraphOS plan. You can test it out by signing up for a Free plan. To compare GraphOS feature support across all plan types, see the pricing page.

With external coprocessing, you can hook into the GraphOS Router's request-handling lifecycle by writing standalone code in any language and framework. This code (i.e., your coprocessor) can run anywhere on your network that's accessible to the router over HTTP.

You can configure your router to "call out" to your coprocessor at different stages throughout the request-handling lifecycle, enabling you to perform custom logic based on a client request's headers, query string, and other details. This logic can access disk and perform network requests, all while safely isolated from the critical router process.

When your coprocessor responds to these requests, its response body can modify various details of the client's request or response. You can even terminate a client request.

Recommended locations for hosting your coprocessor include:

  • On the same host as your router (minimal request latency)

  • In the same Pod as your router, as a "sidecar" container (minimal request latency)

  • In the same availability zone as your router (low request latency with increased deployment isolation)

How it works

Whenever your router receives a client request, at various stages in the request-handling lifecycle it can send HTTP POST requests to your coprocessor:

This diagram shows request execution proceeding "down" from a client, through the router, to individual subgraphs. Execution then proceeds back "up" to the client in the reverse order.

As shown in the diagram above, the RouterService, SupergraphService, ExecutionService, and SubgraphService steps of the request-handling lifecycle can send these POST requests (also called coprocessor requests).

Each supported service can send its coprocessor requests at two different stages:

  • As execution proceeds "down" from the client to individual subgraphs

    • Here, the coprocessor can inspect and modify details of requests before GraphQL operations are processed.

    • The coprocessor can also instruct the router to terminate a client request immediately.

  • As execution proceeds back "up" from subgraphs to the client

    • Here, the coprocessor can inspect and modify details of the router's response to the client.

At every stage, the router waits for your coprocessor's response before it continues processing the corresponding request. Because of this, you should maximize responsiveness by configuring only whichever coprocessor requests your customization requires.

Multiple requests with SubgraphService

If your coprocessor hooks into your router's SubgraphService, the router sends a separate coprocessor request for each subgraph request in its query plan. In other words, if your router needs to query three separate subgraphs to fully resolve a client operation, it sends three separate coprocessor requests. Each coprocessor request includes the name and URL of the subgraph being queried.

Setup

First, make sure your router is connected to a GraphOS organization.

You configure external coprocessing in your router's YAML config file, under the coprocessor key.

Typical configuration

This example configuration sends commonly used request and response details to your coprocessor (see the comments below for explanations of each field):

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:8081 # Required. Replace with the URL of your coprocessor's HTTP endpoint.
3  timeout: 2s # The timeout for all coprocessor requests. Defaults to 1 second (1s)
4  router: # This coprocessor hooks into the `RouterService`
5    request: # By including this key, the `RouterService` sends a coprocessor request whenever it first receives a client request.
6      headers: true # These boolean properties indicate which request data to include in the coprocessor request. All are optional and false by default.
7      body: false
8      context: false
9      sdl: false
10      path: false
11      method: false
12    response: # By including this key, the `RouterService` sends a coprocessor request whenever it's about to send response data to a client (including incremental data via @defer).
13      headers: true
14      body: false
15      context: false
16      sdl: false
17      status_code: false
18  supergraph: # This coprocessor hooks into the `SupergraphService`
19    request: # By including this key, the `SupergraphService` sends a coprocessor request whenever it first receives a client request.
20      headers: true # These boolean properties indicate which request data to include in the coprocessor request. All are optional and false by default.
21      body: false
22      context: false
23      sdl: false
24      method: false
25    response: # By including this key, the `SupergraphService` sends a coprocessor request whenever it's about to send response data to a client (including incremental data via @defer).
26      headers: true
27      body: false
28      context: false
29      sdl: false
30      status_code: false
31  subgraph:
32    all:
33      request: # By including this key, the `SubgraphService` sends a coprocessor request whenever it is about to make a request to a subgraph.
34        headers: true # These boolean properties indicate which request data to include in the coprocessor request. All are optional and false by default.
35        body: false
36        context: false
37        uri: false
38        method: false
39        service_name: false
40        subgraph_request_id: false
41      response: # By including this key, the `SubgraphService` sends a coprocessor request whenever receives a subgraph response.
42        headers: true
43        body: false
44        context: false
45        service_name: false
46        status_code: false
47        subgraph_request_id: false

Minimal configuration

You can confirm that your router can reach your coprocessor by setting this minimal configuration before expanding it as needed:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:8081 # Replace with the URL of your coprocessor's HTTP endpoint.
3  router:
4    request:
5      headers: false

In this case, the RouterService only sends a coprocessor request whenever it receives a client request. The coprocessor request body includes no data related to the client request (only "control" data, which is covered below).

Conditions

You can define conditions for a stage of the request lifecycle that you want to run the coprocessor. You can set coprocessor conditions with selectors based on headers or context entries.

note
The Execution stage doesn't support coprocessor conditions.

Example configurations:

  • Run during the SupergraphResponse stage only for the first event of a supergraph response. Useful for handling only the first subscription event when a subscription is opened:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:3000
3  supergraph:
4    response:
5      condition:
6        eq:
7          - true
8          - is_primary_response: true # Will be true only for the first event received on a supergraph response (like classical queries and mutations for example)
9      body: true
10      headers: true

  • Run during the Request stage only if the request contains a request header:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:3000
3  router:
4    request:
5      condition:
6        eq:
7          - request_header: should-execute-copro # Header name
8          - "enabled" # Header value
9      body: true
10      headers: true

Context configuration

The router request context is used to share data across stages of the request pipeline. The coprocessor can also use this context. By default, the context is not sent to the coprocessor (context: false). You can send all context keys to your coprocessor using context: all. You can also specify exactly which context keys you wish to send to a coprocessor by listing them under the selective key. This will reduce the size of the request/response and may improve performance.

If you're upgrading from router 1.x, the context key names changed in router v2.0. You can specify context: deprecated to send all context with the old names, compatible with v1.x. Context keys are translated to their v1.x names before being sent to the coprocessor, and translated back to the v2.x names after being received from the coprocessor.

note
context: true from router 1.x is still supported by the configuration, and is an alias for context: deprecated. We strongly recommend using context: deprecated or context: all instead.

Example:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:3000 # mandatory URL which is the address of the coprocessor
3  router:
4    request:
5      context: false # Do not send any context entries
6  supergraph:
7    request:
8      headers: true
9      context: # It will only send these 2 context keys to your coprocessor
10        selective:
11          - apollo::supergraph::operation_name
12          - apollo::demand_control::actual_cost
13      body: true
14    response:
15      headers: true
16      context: all # It will send all context keys with new names (2.x version)
17      body: true
18  subgraph:
19    all:
20      request:
21        context: deprecated # It will send all the context keys with deprecated names (1.x version)
note
If you use the selective configuration, you must use the new context key names from v2.x. It does not support the deprecated keys from v1.x. So for example, if you try to specify operation_name instead of apollo::supergraph::operation_name, it won't map to the new context key.

Client configuration

The router supports coprocessor connections over:

  • HTTP/1.1
  • HTTP/1.1 with TLS
  • HTTP/2 with TLS
  • HTTP/2 Cleartext protocol (h2c). This uses HTTP/2 over plaintext connections.

Use the table below to look up the resulting protocol of a coprocessor connection, based on the URL and the experimental_http2 configuration:

URL with http://URL with https://
experimental_http2: disableHTTP/1.1HTTP/1.1 with TLS
experimental_http2: enableHTTP/1.1Either HTTP/1.1 or HTTP/2 with TLS, as determined by the TLS handshake
experimental_http2: http2onlyh2cHTTP/2 with TLS
experimental_http2
not set		HTTP/1.1Either HTTP/1.1 or HTTP/2 with TLS, as determined by the TLS handshake
note

Configuring experimental_http2: http2only for a network that doesn't support HTTP/2 results in a failed coprocessor connection.

For example, to enable h2c (http2 cleartext) communication with a coprocessor you can use this configuration:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:8081
3  # Using an HTTP (not HTTPS) URL and experimental_http2: http2only results in connections that use h2c
4  client:
5    experimental_http2: http2only

Coprocessor request format

The router communicates with your coprocessor via HTTP POST requests (called coprocessor requests). The body of each coprocessor request is a JSON object with properties that describe either the current client request or the current router response.

note
Body properties vary by the router's current execution stage. See example request bodies for each stage.

Properties of the JSON body are divided into two high-level categories:

  • "Control" properties

    • These provide information about the context of the specific router request or response. They provide a mechanism to influence the router's execution flow.

    • The router always includes these properties in coprocessor requests.

  • Data properties

    • These provide information about the substance of a request or response, such as the GraphQL query string and any HTTP headers. Aside from sdl, your coprocessor can modify all of these properties.

    • You configure which of these fields the router includes in its coprocessor requests. By default, the router includes none of them.

Example requests by stage

RouterRequest

Click to expand
JSON
Example coprocessor request body
1{
2  // Control properties
3  "version": 1,
4  "stage": "RouterRequest",
5  "control": "continue",
6  "id": "1b19c05fdafc521016df33148ad63c1b",
7
8  // Data properties
9  "headers": {
10    "cookie": [
11      "tasty_cookie=strawberry"
12    ],
13    "content-type": [
14      "application/json"
15    ],
16    "host": [
17      "127.0.0.1:4000"
18    ],
19    "apollo-federation-include-trace": [
20      "ftv1"
21    ],
22    "apollographql-client-name": [
23      "manual"
24    ],
25    "accept": [
26      "*/*"
27    ],
28    "user-agent": [
29      "curl/7.79.1"
30    ],
31    "content-length": [
32      "46"
33    ]
34  },
35  "body": "{
36    \"query\": \"query GetActiveUser {\n  me {\n  name\n}\n}\"
37  }",
38  "context": {
39    "entries": {
40      "accepts-json": false,
41      "accepts-wildcard": true,
42      "accepts-multipart": false
43    }
44  },
45  "sdl": "...", // String omitted due to length
46  "path": "/",
47  "method": "POST"
48}

RouterResponse

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "RouterResponse",
5  "control": "continue",
6  "id": "1b19c05fdafc521016df33148ad63c1b",
7
8  // Data properties
9  "headers": {
10    "vary": [
11      "origin"
12    ],
13    "content-type": [
14      "application/json"
15    ]
16  },
17  "body": "{
18    \"data\": {
19      \"me\": {
20        \"name\": \"Ada Lovelace\"
21      }
22    }
23  }",
24  "context": {
25    "entries": {
26      "apollo_telemetry::subgraph_metrics_attributes": {},
27      "accepts-json": false,
28      "accepts-multipart": false,
29      "apollo::telemetry::client_name": "manual",
30      "apollo_telemetry::usage_reporting": {
31        "statsReportKey": "# Long\nquery Long{me{name}}",
32        "referencedFieldsByType": {
33          "User": {
34            "fieldNames": [
35              "name"
36            ],
37            "isInterface": false
38          },
39          "Query": {
40            "fieldNames": [
41              "me"
42            ],
43            "isInterface": false
44          }
45        }
46      },
47      "apollo::telemetry::client_version": "",
48      "accepts-wildcard": true
49    }
50  },
51  "statusCode": 200,
52  "sdl": "..." // Omitted due to length
53}

SupergraphRequest

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "SupergraphRequest",
5  "control": "continue",
6
7  // Data properties
8  "headers": {
9    "cookie": ["tasty_cookie=strawberry"],
10    "content-type": ["application/json"],
11    "host": ["127.0.0.1:4000"],
12    "apollo-federation-include-trace": ["ftv1"],
13    "apollographql-client-name": ["manual"],
14    "accept": ["*/*"],
15    "user-agent": ["curl/7.79.1"],
16    "content-length": ["46"]
17  },
18  "body": {
19    "query": "query Long {\n  me {\n  name\n}\n}",
20    "operationName": "MyQuery",
21    "variables": {}
22  },
23  "context": {
24    "entries": {
25      "accepts-json": false,
26      "accepts-wildcard": true,
27      "accepts-multipart": false,
28      "this-is-a-test-context": 42
29    }
30  },
31  "serviceName": "service name shouldn't change",
32  "uri": "http://thisurihaschanged"
33}

SupergraphResponse

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "SupergraphResponse",
5  "control": {
6    "break": 200
7  },
8
9  // Data properties
10  "body": {
11    "errors": [{ "message": "my error message" }]
12  },
13  "context": {
14    "entries": {
15      "testKey": true
16    }
17  },
18  "headers": {
19    "aheader": ["a value"]
20  }
21}

ExecutionRequest

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "ExecutionRequest",
5  "control": "continue",
6
7  // Data properties
8  "headers": {
9    "cookie": ["tasty_cookie=strawberry"],
10    "content-type": ["application/json"],
11    "host": ["127.0.0.1:4000"],
12    "apollo-federation-include-trace": ["ftv1"],
13    "apollographql-client-name": ["manual"],
14    "accept": ["*/*"],
15    "user-agent": ["curl/7.79.1"],
16    "content-length": ["46"]
17  },
18  "body": {
19    "query": "query Long {\n  me {\n  name\n}\n}",
20    "operationName": "MyQuery"
21  },
22  "context": {
23    "entries": {
24      "accepts-json": false,
25      "accepts-wildcard": true,
26      "accepts-multipart": false,
27      "this-is-a-test-context": 42
28    }
29  },
30  "serviceName": "service name shouldn't change",
31  "uri": "http://thisurihaschanged",
32  "queryPlan": {
33    "usage_reporting": {
34      "statsReportKey": "# Me\nquery Me{me{name username}}",
35      "referencedFieldsByType": {
36        "User": { "fieldNames": ["name", "username"], "isInterface": false },
37        "Query": { "fieldNames": ["me"], "isInterface": false }
38      }
39    },
40    "root": {
41      "kind": "Fetch",
42      "serviceName": "accounts",
43      "variableUsages": [],
44      "operation": "query Me__accounts__0{me{name username}}",
45      "operationName": "Me__accounts__0",
46      "operationKind": "query",
47      "id": null,
48      "inputRewrites": null,
49      "outputRewrites": null,
50      "authorization": {
51        "is_authenticated": false,
52        "scopes": [],
53        "policies": []
54      }
55    },
56    "formatted_query_plan": "QueryPlan {\n  Fetch(service: \"accounts\") {\n    {\n      me {\n        name\n        username\n      }\n    }\n  },\n}",
57    "query": {
58      "string": "query Me {\n  me {\n    name\n    username\n  }\n}\n",
59      "fragments": { "map": {} },
60      "operations": [
61        {
62          "name": "Me",
63          "kind": "query",
64          "type_name": "Query",
65          "selection_set": [
66            {
67              "Field": {
68                "name": "me",
69                "alias": null,
70                "selection_set": [
71                  {
72                    "Field": {
73                      "name": "name",
74                      "alias": null,
75                      "selection_set": null,
76                      "field_type": { "Named": "String" },
77                      "include_skip": { "include": "Yes", "skip": "No" }
78                    }
79                  },
80                  {
81                    "Field": {
82                      "name": "username",
83                      "alias": null,
84                      "selection_set": null,
85                      "field_type": { "Named": "String" },
86                      "include_skip": { "include": "Yes", "skip": "No" }
87                    }
88                  }
89                ],
90                "field_type": { "Named": "User" },
91                "include_skip": { "include": "Yes", "skip": "No" }
92              }
93            }
94          ],
95          "variables": {}
96        }
97      ],
98      "subselections": {},
99      "unauthorized": {
100        "paths": [],
101        "errors": { "log": true, "response": "errors" }
102      },
103      "filtered_query": null,
104      "defer_stats": {
105        "has_defer": false,
106        "has_unconditional_defer": false,
107        "conditional_defer_variable_names": []
108      },
109      "is_original": true
110    }
111  }
112}

ExecutionResponse

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "ExecutionResponse",
5  "control": {
6    "break": 200
7  },
8
9  // Data properties
10  "body": {
11    "errors": [{ "message": "my error message" }]
12  },
13  "context": {
14    "entries": {
15      "testKey": true
16    }
17  },
18  "headers": {
19    "aheader": ["a value"]
20  }
21}

SubgraphRequest

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "SubgraphRequest",
5  "control": "continue",
6  "id": "666d677225c1bc6d7c54a52b409dbd4e",
7  "subgraphRequestId": "b5964998b2394b64a864ef802fb5a4b3",
8
9  // Data properties
10  "headers": {},
11  "body": {
12    "query": "query TopProducts__reviews__1($representations:[_Any!]!){_entities(representations:$representations){...on Product{reviews{body id}}}}",
13    "operationName": "TopProducts__reviews__1",
14    "variables": {
15      "representations": [
16        {
17          "__typename": "Product",
18          "upc": "1"
19        },
20        {
21          "__typename": "Product",
22          "upc": "2"
23        },
24        {
25          "__typename": "Product",
26          "upc": "3"
27        }
28      ]
29    }
30  },
31  "context": {
32    "entries": {
33      "apollo_telemetry::usage_reporting": {
34        "statsReportKey": "# TopProducts\nquery TopProducts{topProducts{name price reviews{body id}}}",
35        "referencedFieldsByType": {
36          "Query": {
37            "fieldNames": ["topProducts"],
38            "isInterface": false
39          },
40          "Review": {
41            "fieldNames": ["body", "id"],
42            "isInterface": false
43          },
44          "Product": {
45            "fieldNames": ["price", "name", "reviews"],
46            "isInterface": false
47          }
48        }
49      },
50      "apollo::telemetry::client_version": "",
51      "apollo_telemetry::subgraph_metrics_attributes": {},
52      "apollo::telemetry::client_name": ""
53    }
54  },
55  "uri": "https://reviews.demo.starstuff.dev/",
56  "method": "POST",
57  "serviceName": "reviews"
58}

SubgraphResponse

Click to expand
JSON
1{
2  // Control properties
3  "version": 1,
4  "stage": "SubgraphResponse",
5  "id": "b7810c6f7f95640fd6c6c8781e3953c0",
6  "subgraphRequestId": "b5964998b2394b64a864ef802fb5a4b3",
7  "control": "continue",
8
9  // Data properties
10  "headers": {
11    "etag": ["W/\"d3-7aayASjs0+e2c/TpiAYgEu/yyo0\""],
12    "via": ["2 fly.io"],
13    "server": ["Fly/90d459b3 (2023-03-07)"],
14    "date": ["Thu, 09 Mar 2023 14:28:46 GMT"],
15    "x-powered-by": ["Express"],
16    "x-ratelimit-limit": ["10000000"],
17    "access-control-allow-origin": ["*"],
18    "x-ratelimit-remaining": ["9999478"],
19    "content-type": ["application/json; charset=utf-8"],
20    "fly-request-id": ["01GV3CCG5EM3ZNVZD2GH0B00E2-lhr"],
21    "x-ratelimit-reset": ["1678374007"]
22  },
23  "body": {
24    "data": {
25      "_entities": [
26        {
27          "reviews": [
28            {
29              "body": "Love it!",
30              "id": "1"
31            },
32            {
33              "body": "Prefer something else.",
34              "id": "4"
35            }
36          ]
37        },
38        {
39          "reviews": [
40            {
41              "body": "Too expensive.",
42              "id": "2"
43            }
44          ]
45        },
46        {
47          "reviews": [
48            {
49              "body": "Could be better.",
50              "id": "3"
51            }
52          ]
53        }
54      ]
55    }
56  },
57  "context": {
58    "entries": {
59      "apollo_telemetry::usage_reporting": {
60        "statsReportKey": "# TopProducts\nquery TopProducts{topProducts{name price reviews{body id}}}",
61        "referencedFieldsByType": {
62          "Product": {
63            "fieldNames": ["price", "name", "reviews"],
64            "isInterface": false
65          },
66          "Query": {
67            "fieldNames": ["topProducts"],
68            "isInterface": false
69          },
70          "Review": {
71            "fieldNames": ["body", "id"],
72            "isInterface": false
73          }
74        }
75      },
76      "apollo::telemetry::client_version": "",
77      "apollo_telemetry::subgraph_metrics_attributes": {},
78      "apollo::telemetry::client_name": ""
79    }
80  },
81  "serviceName": "reviews",
82  "statusCode": 200
83}

Property reference

Property / Type Description
Control properties
control
string | object		Indicates whether the router should continue processing the current client request. In coprocessor request bodies from the router, this value is always the string value continue.In your coprocessor's response, you can instead return an object with the following format:
JSON
1{ "break": 400 }
If you do this, the router terminates the request-handling lifecycle and immediately responds to the client with the provided HTTP code and response body you specify.For details, see Terminating a client request.
id
string		A unique ID corresponding to the client request associated with this coprocessor request.Do not return a different value for this property. If you do, the router treats the coprocessor request as if it failed.
subgraphRequestId
string		A unique ID corresponding to the subgraph request associated with this coprocessor request (only available at the SubgraphRequest and SubgraphResponse stages).Do not return a different value for this property. If you do, the router treats the coprocessor request as if it failed.
stage
string		Indicates which stage of the router's request-handling lifecycle this coprocessor request corresponds to.This value is one of the following:
  • RouterRequest: The RouterService has just received a client request.
  • RouterResponse: The RouterService is about to send response data to a client.
  • SupergraphRequest: The SupergraphService is about to send a GraphQL request.
  • SupergraphResponse: The SupergraphService has just received a GraphQL response.
  • SubgraphRequest: The SubgraphService is about to send a request to a subgraph.
  • SubgraphResponse: The SubgraphService has just received a subgraph response.
Do not return a different value for this property. If you do, the router treats the coprocessor request as if it failed.
version
number		Indicates which version of the coprocessor request protocol the router is using.Currently, this value is always 1.Do not return a different value for this property. If you do, the router treats the coprocessor request as if it failed.
Data properties
body
string | object		The body of the corresponding request or response.This field is populated when the underlying HTTP method is POST. If you are looking for operation data on GET requests, that info will be populated in the path parameter per the GraphQL over HTTP spec.If your coprocessor returns a different value for body, the router replaces the existing body with that value. This is common when terminating a client request.This field's type depends on the coprocessor request's stage:
  • For SubgraphService stages, body is a JSON object.
  • For SupergraphService stages, body is a JSON object.
  • For RouterService stages, body is a JSON string.
    • This is necessary to support handling deferred queries.
    • If you modify body during the RouterRequest stage, the new value must be a valid string serialization of a JSON object. If it isn't, the router detects that the body is malformed and returns an error to the client.
This field's structure depends on whether the coprocessor request corresponds to a request, a standard response, or a response "chunk" for a deferred query:
  • If a request, body usually contains a query property containing the GraphQL query string.
  • If a standard response, body usually contains data and/or errors properties for the GraphQL operation result.
  • If a response "chunk", body contains data for some of the operation fields.
By default, the RouterResponse stage returns redacted errors within the errors field. To process subgraph errors manually in your coprocessor, enable subgraph error inclusion.
context
object		An object representing the router's shared context for the corresponding client request.If your coprocessor returns a different value for context, the router replaces the existing context with that value.
hasNext
bool		When stage is SupergraphResponse, if present and true then there will be subsequent SupergraphResponse calls to the co-processor for each multi-part (@defer/subscriptions) response.
headers
object		An object mapping of all HTTP header names and values for the corresponding request or response.Ensure headers are handled like HTTP headers in general. For example, normalize header case before your coprocessor operates on them.If your coprocessor returns a different value for headers, the router replaces the existing headers with that value.
The router discards any content-length headers sent by coprocessors because incorrect content-length values can lead to HTTP request failures.
method
string		The HTTP method that is used by the request.
path
string		The RouterService or SupergraphService path that this coprocessor request pertains to.
sdl
string		A string representation of the router's current supergraph schema.This value can be very large, so you should avoid including it in coprocessor requests if possible.The router ignores modifications to this value.
serviceName
string		The name of the subgraph that this coprocessor request pertains to.This value is present only for coprocessor requests from the router's SubgraphService.Do not return a different value for this property. If you do, the router treats the coprocessor request as if it failed.
statusCode
number		The HTTP status code returned with a response.
uri
string		When stage is SubgraphRequest, this is the full URI of the subgraph the router will query.
query_plan
string		When stage is ExecutionRequest, this contains the query plan for the client query. It cannot be modified by the coprocessor.

Responding to coprocessor requests

The router expects your coprocessor to respond with a 200 status code and a JSON body that matches the structure of the request body.

In the response body, your coprocessor can return modified values for certain properties. By doing so, you can modify the remainder of the router's execution for the client request.

The router supports modifying the following properties from your coprocessor:

caution
Do not modify other control properties. Doing so can cause the client request to fail.

If you omit a property from your response body entirely, the router uses its existing value for that property.

Terminating a client request

Every coprocessor request body includes a control property with the string value continue. If your coprocessor's response body also sets control to continue, the router continues processing the client request as usual.

Alternatively, your coprocessor's response body can set control to an object with a break property, like so:

JSON
1{
2  "control": { "break": 401 },
3  "body": {
4    "errors": [
5      {
6        "message": "Not authenticated.",
7        "extensions": {
8          "code": "ERR_UNAUTHENTICATED"
9        }
10      }
11    ]
12  }
13}

If the router receives an object with this format for control, it immediately terminates the request-handling lifecycle for the client request. It sends an HTTP response to the client with the following details:

  • The HTTP status code is set to the value of the break property (401 in the example above).

  • The response body is the coprocessor's returned value for body.

    • The value of body should adhere to the standard GraphQL JSON response format (see the example above).

    • Alternatively, you can specify a string value for body. If you do, the router returns an error response with that string as the error's message.

The example response above sets the HTTP status code to 400, which indicates a failed request.

You can also use this mechanism to immediately return a successful response:

JSON
1{
2  "control": { "break": 200 },
3  "body": {
4    "data": {
5      "currentUser": {
6        "name": "Ada Lovelace"
7      }
8    }
9  }
10}
note
If you return a successful response, make sure the structure of the data property matches the structure expected by the client query.
tip
The body in the RouterRequest and RouterResponse stages is always a string, but you can still break with a GraphQL response if it's encoded as JSON.
Examples of coprocessor responses for Router stages
JSON
1{
2  "control": { "break": 500 },
3  "body": "{ \"errors\": [ { \"message\": \"Something went wrong\", \"extensions\": { \"code\": \"INTERNAL_SERVER_ERRROR\" } } ] }"
4}
JSON
1{
2  "control": { "break": 200 },
3  "body": "{ \"data\": { \"currentUser\": { \"name\": \"Ada Lovelace\" } }"
4}
note
If you return a successful response, make sure the structure of the data property matches the structure expected by the client query.

Failed responses

If a request to a coprocessor results in a failed response, which is seperate from a control break, the router will return an error to the client making the supergraph request. The router considers all of the following scenarios to be a failed response from your coprocessor:

  • Your coprocessor doesn't respond within the amount of time specified by the timeout key in your configuration (default one second).

  • Your coprocessor responds with a non-2xx HTTP code.

  • Your coprocessor's response body doesn't match the JSON structure of the corresponding request body.

  • Your coprocessor's response body sets different values for control properties that must not change, such as stage and version.

Handling deferred query responses

GraphOS Router and Apollo Router Core support the incremental delivery of query response data via the @defer directive:

For a single query with deferred fields, your router sends multiple "chunks" of response data to the client. If you enable coprocessor requests for the RouterResponse stage, your router sends a separate coprocessor request for each chunk it returns as part of a deferred query.

Note the following about handling deferred response chunks:

  • The status_code and headers fields are included only in the coprocessor request for any response's first chunk. These values can't change after the first chunk is returned to the client, so they're subsequently omitted.

  • If your coprocessor modifes the response body for a response chunk, it must provide the new value as a string, not as an object. This is because response chunk bodies include multipart boundary information in addition to the actual serialized JSON response data. See examples.

    • Many responses will not contain deferred streams and for these the body string can usually be fairly reliably transformed into a JSON object for easy manipulation within the coprocessor. Coprocessors should be carefully coded to allow for the presence of a body that is not a valid JSON object.

  • Because the data is a JSON string at both RouterRequest and RouterResponse, it's entirely possible for a coprocessor to rewrite the body from invalid JSON content into valid JSON content. This is one of the primary use cases for RouterRequest body processing.

Examples of deferred response chunks

The examples below illustrate the differences between the first chunk of a deferred response and all subsequent chunks:

First response chunk

The first response chunk includes headers and statusCode fields:

JSON
1{
2  "version": 1,
3  "stage": "RouterResponse",
4  "id": "8dee7fe947273640a5c2c7e1da90208c",
5  "sdl": "...", // String omitted due to length
6  "headers": {
7    "content-type": ["multipart/mixed;boundary=\"graphql\";deferSpec=20220824"],
8    "vary": ["origin"]
9  },
10  "body": "\r\n--graphql\r\ncontent-type: application/json\r\n\r\n{\"data\":{\"me\":{\"id\":\"1\"}},\"hasNext\":true}\r\n--graphql\r\n",
11  "context": {
12    "entries": {
13      "apollo::supergraph::operation_kind": "query",
14      "apollo::telemetry::client_version": "",
15      "apollo::telemetry::client_name": "manual"
16    }
17  },
18  "statusCode": 200
19}

Subsequent response chunk

Subsequent response chunks omit the headers and statusCode fields:

JSON
1{
2  "version": 1,
3  "stage": "RouterResponse",
4  "id": "8dee7fe947273640a5c2c7e1da90208c",
5  "sdl": "...", // String omitted due to length
6  "body": "content-type: application/json\r\n\r\n{\"hasNext\":false,\"incremental\":[{\"data\":{\"name\":\"Ada Lovelace\"},\"path\":[\"me\"]}]}\r\n--graphql--\r\n",
7  "context": {
8    "entries": {
9      "apollo::supergraph::operation_kind": "query",
10      "apollo::telemetry::client_version": "",
11      "apollo::telemetry::client_name": "manual"
12    }
13  }
14}

Adding authorization claims via coprocessor

To use the authorization directives, a request needs to include claims—the details of its authentication and scope. The most straightforward way to add claims is with JWT authentication. You can also add claims with a RouterService or SupergraphService coprocessor since they hook into the request lifecycle before the router applies authorization logic.

An example configuration of the router calling a coprocessor for authorization claims:

YAML
router.yaml
1coprocessor:
2  url: http://127.0.0.1:8081 # Required. Replace with the URL of your coprocessor's HTTP endpoint.
3  router: # By including this key, a coprocessor can hook into the `RouterService`. You can also use `SupergraphService` for authorization.
4    request: # By including this key, the `RouterService` sends a coprocessor request whenever it first receives a client request.
5      headers: false # These boolean properties indicate which request data to include in the coprocessor request. All are optional and false by default.
6      context: all # The authorization directives works with claims stored in the request's context

This configuration prompts the router to send an HTTP POST request to your coprocessor whenever it receives a client request. For example, your coprocessor may receive a request with this format:

JSON
1{
2  "version": 1,
3  "stage": "RouterRequest",
4  "control": "continue",
5  "id": "d0a8245df0efe8aa38a80dba1147fb2e",
6  "context": {
7    "entries": {
8      "accepts-json": true
9    }
10  }
11}

When your coprocessor receives this request from the router, it should add claims to the request's context and return them in the response to the router. Specifically, the coprocessor should add an entry with a claims object. The key must be apollo::authentication::jwt_claims, and the value should be the claims required by the authorization directives you intend to use. For example, if you want to use @requireScopes, the response may look something like this:

JSON
1{
2  "version": 1,
3  "stage": "RouterRequest",
4  "control": "continue",
5  "id": "d0a8245df0efe8aa38a80dba1147fb2e",
6  "context": {
7    "entries": {
8      "accepts-json": true,
9      "apollo::authentication::jwt_claims": {
10        "scope": "profile:read profile:write"
11      }
12    }
13  }
14}

Additional resources

note
The code in this repository is experimental and has been provided for reference purposes only.
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