HTTP Function Endpoint
This documentation is for an unreleased version of Apache Flink Stateful Functions. We recommend you use the latest stable version.

HTTP Function Endpoint #

An HTTP Function Endpoint component defines the endpoint URL that the Stateful Functions runtime should connect to for invoking a given function, or for a more dynamic deployment, functions within a specified namespace.

Below is an example of an HTTP endpoint definition in an application’s module configuration:

kind: io.statefun.endpoints.v2/http
spec:
  functions: com.example/*
  urlPathTemplate: https://bar.foo.com:8080/{function.name}
  transport:
    timeouts:
      call: 1 min
      read: 10 sec
      write: 10 sec
kind: io.statefun.endpoints.v1/http
spec:
  functions: com.example/*
  urlPathTemplate: https://bar.foo.com:8080/{function.name}
  timeouts:
    call: 1 min
    read: 10 sec
    write: 10 sec

In this example, an endpoint for a function within the logical namespace com.example is declared. The runtime will invoke all functions under this namespace with the endpoint URL template.

URL Template #

The URL template name may contain template parameters filled in dynamically based on the function’s specific type. In the example below, a message sent to message type com.example/greeter will be sent to http://bar.foo.com/greeter.

spec:
  functions: com.example/*
  urlPathTemplate: https://bar.foo.com/{function.name}

Templating parameterization works well with load balancers and service gateways. Suppose http://bar.foo.com was an NGINX server; you can use the different paths to physical systems. Users may now deploy some functions on Kubernetes, others AWS Lambda, while others are still on physical servers.

function dispatch

Transport #

Switching between different transport clients is supported since v2 of HTTP function endpoint definitions.

The transport client to use is specified using spec.transport.type. If not specified, by default, Stateful Functions uses OkHttp.

All fields under spec.transport is used as the properties to configure the transport client. For example, the example below configures various timeout settings for the default OkHttp transport:

spec:
  transport:
    timeouts:
      call: 1 min
      read: 30 sec
      write: 20 sec

Asynchronous HTTP transport (Beta) #

Alternatively, Stateful Functions also ships a transport option based on asynchronous non-blocking IO, implemented with Netty. This transport enables much higher resource utilization, higher throughput, and lower remote function invocation latency.

Below is a complete example of the transport section of an HTTP function endpoint definition, if you want to use this transport type:

spec:
  transport:
    type: io.statefun.transports.v1/async
    call: 2m
    connect: 20s
    pool_ttl: 15s
    pool_size: 1024
    payload_max_bytes: 33554432

Please see the full spec options below for a description of each property.

Full Spec Options #

Target functions (or function) #

The meta typename is the logical type name used to match a function invocation with a physical endpoint. Typenames are composed of a namespace (required) and name (optional). Endpoints containing a namespace but no name will match all function types in that namespace.

It is recommended to have endpoints only specified against a namespace to enable dynamic function registration.
spec:
  functions: com.example/*

Url Path Template #

The urlPathTemplate is the physical path to be resolved when an endpoint is matched. It may contain templated parameters for dynamic routing.

spec:
  urlPathTemplate: http://bar.foo.com/{function.name}

Supported schemes:

  • http
  • https

Transport via UNIX domain sockets is supported by using the schemes http+unix or https+unix. When using UNIX domain sockets, the endpoint format is: http+unix://<socket-file-path>/<serve-url-path>. For example, http+unix:///uds.sock/path/of/url. For example, http+unix:///uds.sock/path/of/url.

Max Batch Requests #

The maximum number of records that can be processed by a function for a particular address (typename + id) before invoking backpressure on the system. The default value is 1000.

spec:
  maxNumBatchRequests: 1000

Transport #

The transport client type to use for sending requests to the function. If not specified, by default, Stateful Functions uses OkHttp.

Below is a full example for configuring the default transport:

spec:
  transport:
    timeouts:
      call: 2m
      connect: 20s
      read: 10s
      write: 10s
  • call: The timeout for a complete function call. This configuration spans the entire call: resolving DNS, connecting, writing the request body, server processing, and reading the response body. If the call requires redirects or retries all must complete within one timeout period. Default value is 1 minute.
  • connect: The default connect timeout for new connections. The connect timeout is applied when connecting a TCP socket to the target host. Default value is 10 seconds.
  • read: The default read timeout for new connections. The read timeout is applied to both the TCP socket and for individual read IO operations. Default value is 10 seconds.
  • write: The default write timeout for new connections. The write timeout is applied for individual write IO operations. Default value is 10 seconds.

Alternatively, a transport client based on asynchronous non-blocking IO is supported:

spec:
  transport:
    type: io.statefun.transports.v1/async
    call: 2m
    connect: 20s
    pool_ttl: 15s
    pool_size: 1024
    payload_max_bytes: 33554432
  • call: total duration of a single request (including retries, and backoffs). After this duration, the call is considered failed.
  • connect: the total amount of time to wait for a successful TCP connection. After that amount of time, an attempt is considered failed, and if the total call time has not elapsed, an additional attempt will be scheduled (after a backoff).
  • pool_ttl: the amount of time a connection will live in the connection pool. Set to 0 to disable, otherwise the connection will be evicted from the pool after (approximately) that time. If a connection is evicted while it is serving a request, that connection will be only marked for eviction and will be dropped from the pool once the request returns.
  • pool_size: the maximum pool size.
  • payload_max_bytes: the maximum size for a request or response payload size. The default is set to 32MB.
We highly recommend setting statefun.async.max-per-task to a much higher value (see Configurations) when using the asynchronous transport type. This configuration dictates the maximum amount of in-flight requests sent to the function before applying back pressure. The default value of this configuration is 1024, which makes sense only for the default threaded blocking OkHttp transport. For the asynchronous transport, a much higher value is recommended.