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Forward request

  • Чланак

APPLIES TO: All API Management tiers

The forward-request policy forwards the incoming request to the backend service specified in the request context. The backend service URL is specified in the API settings and can be changed using the set backend service policy.

Important

  • This policy is required to forward requests to an API backend. By default, API Management sets up this policy at the global scope.
  • Removing this policy results in the request not being forwarded to the backend service. Policies in the outbound section are evaluated immediately upon the successful completion of the policies in the inbound section.

Note

Set the policy's elements and child elements in the order provided in the policy statement. Learn more about how to set or edit API Management policies.

Policy statement

<forward-request http-version="1 | 2or1 | 2" timeout="time in seconds (alternatively, use timeout-ms)" | timeout-ms="time in milliseconds (alternatively, use timeout)" continue-timeout="time in seconds" follow-redirects="false | true" buffer-request-body="false | true" buffer-response="true | false" fail-on-error-status-code="false | true"/>

Attributes

Attribute Description Required Default
timeout The amount of time in seconds to wait for the HTTP response headers to be returned by the backend service before a timeout error is raised. Minimum value is 0 seconds. Values greater than 240 seconds may not be honored, because the underlying network infrastructure can drop idle connections after this time. Policy expressions are allowed. You can specify either timeout or timeout-ms but not both. No 300
timeout-ms The amount of time in milliseconds to wait for the HTTP response headers to be returned by the backend service before a timeout error is raised. Minimum value is 0 ms. Policy expressions are allowed. You can specify either timeout or timeout-ms but not both. No N/A
continue-timeout The amount of time in seconds to wait for a 100 Continue status code to be returned by the backend service before a timeout error is raised. Policy expressions are allowed. No N/A
http-version The HTTP spec version to use when sending the HTTP response to the backend service. When using 2or1, the gateway will favor HTTP /2 over /1, but fall back to HTTP /1 if HTTP /2 doesn't work. No 1
follow-redirects Specifies whether redirects from the backend service are followed by the gateway or returned to the caller. Policy expressions are allowed. No false
buffer-request-body When set to true, request is buffered and will be reused on retry. No false
buffer-response Affects processing of chunked responses. When set to false, each chunk received from the backend is immediately returned to the caller. When set to true, chunks are buffered (8 KB, unless end of stream is detected) and only then returned to the caller.

Set to false with backends such as those implementing server-sent events (SSE) that require content to be returned or streamed immediately to the caller. Policy expressions aren't allowed.		 No true
fail-on-error-status-code When set to true, triggers on-error section for response codes in the range from 400 to 599 inclusive. Policy expressions aren't allowed. No false

Usage

Examples

Send request to HTTP/2 backend

The following API level policy forwards all API requests to an HTTP/2 backend service.

<!-- api level -->
<policies>
    <inbound>
        <base/>
    </inbound>
    <backend>
        <forward-request http-version="2or1"/>
    </backend>
    <outbound>
        <base/>
    </outbound>
</policies>

This is required for HTTP /2 or gRPC workloads and currently only supported in self-hosted gateway. Learn more in our API gateway overview.

Forward request with timeout interval

The following API level policy forwards all API requests to the backend service with a timeout interval of 60 seconds.

<!-- api level -->
<policies>
    <inbound>
        <base/>
    </inbound>
    <backend>
        <forward-request timeout="60"/>
    </backend>
    <outbound>
        <base/>
    </outbound>
</policies>

Inherit policy from parent scope

This operation level policy uses the base element to inherit the backend policy from the parent API level scope.

<!-- operation level -->
<policies>
    <inbound>
        <base/>
    </inbound>
    <backend>
        <base/>
    </backend>
    <outbound>
        <base/>
    </outbound>
</policies>

Do not inherit policy from parent scope

This operation level policy explicitly forwards all requests to the backend service with a timeout of 120 and doesn't inherit the parent API level backend policy. If the backend service responds with an error status code from 400 to 599 inclusive, on-error section will be triggered.

<!-- operation level -->
<policies>
    <inbound>
        <base/>
    </inbound>
    <backend>
        <forward-request timeout="120" fail-on-error-status-code="true" />
        <!-- effective policy. note the absence of <base/> -->
    </backend>
    <outbound>
        <base/>
    </outbound>
</policies>

Do not forward requests to backend

This operation level policy doesn't forward requests to the backend service.

<!-- operation level -->
<policies>
    <inbound>
        <base/>
    </inbound>
    <backend>
        <!-- no forwarding to backend -->
    </backend>
    <outbound>
        <base/>
    </outbound>
</policies>

Related content

For more information about working with policies, see: