Container runtime contract

This page lists key requirements and behaviors of containers in Cloud Run.

Supported languages and images

Your container image can run code written in the programming language of your choice and use any base image, provided that it respects the constraints listed in this page.

Executables in the container image must be compiled for Linux 64-bit. Cloud Run specifically supports the Linux x86_64 ABI format.

Listening for requests on the correct port

The container must listen for requests on 0.0.0.0 on the port to which requests are sent. By default, requests are sent to 8080, but you can configure Cloud Run to send requests to the port of your choice.

Inside Cloud Run container instances, the value of the PORT environment variable always reflects the port to which requests are sent. It defaults to 8080.

Responses

Your container instance must send a response within the time specified in the request timeout setting after it receives a request, including the container instance startup time. Otherwise the request is ended and a 504 error is returned.

A container instance is terminated if it returns more than 20 5xx sequential responses.

Environment variables

The following environment variables are automatically added to the running containers:

Name Description Example
PORT The port your HTTP server should listen on. 8080
K_SERVICE The name of the Cloud Run service being run. hello-world
K_REVISION The name of the Cloud Run revision being run. hello-world.1
K_CONFIGURATION The name of the Cloud Run configuration that created the revision. hello-world

Filesystem access

The filesystem of your container is writable and is subject to the following behavior:

  • This is an in-memory filesystem, so writing to it uses the container instance's memory.
  • Data written to the filesystem does not persist when the container instance is stopped.

Container instance lifecycle

In response to incoming requests, a service is automatically scaled to a certain number of container instances, each of which runs the deployed container image.

When a revision does not receive any traffic, it is scaled down to the minimum container instances configured (zero by default).

Startup

Your container instances must listen for requests within 4 minutes after being started. During this startup time, container instances are allocated CPU.

Computation is scoped to a request

After startup, you should only expect to be able to do computation within the scope of a request: a container instance does not have any CPU allocated if it is not processing a request.

Shutdown

Container instances can be shut down at any time. When a container instance needs to be shut down, new incoming requests are routed to other instances and requests currently being processed are given time to complete. The container instance then receives a SIGTERM signal indicating the start of a 10 second period before being shut down (with a SIGKILL signal). During this period, the container instance is allocated CPU and billed. If the container instance does not catch the SIGTERM signal, it is immediately shut down.

Container instance resources

CPU

Cloud Run allocates 1 vCPU per container instance by default, but this can be changed.

A vCPU is implemented as an abstraction of underlying hardware to provide the approximate equivalent CPU time of a single hardware hyper-thread on variable CPU platforms. The container instance may be executed on multiple cores simultaneously. The vCPU is only allocated during container instance startup and request processing, it is throttled otherwise.

To allocate a different vCPU value, refer to the documentation for allocating CPU.

Memory

Each Cloud Run container instance by default gets 256 MiB of memory. You can change this by configuring memory limits, up to a maximum of 4 GiB.

Typical uses of memory include:

  • Code loaded into memory to run the service
  • Writing to the filesystem
  • Extra processes running in the container such as an nginx server
  • In-memory caching systems such as the PHP OpCache
  • Per request memory usage

Concurrency

Each Cloud Run container instance by default is set to multiple concurrency, where each container instance can receive more than one request at the same time. You can change this by setting concurrency.

Container instance sandbox

The Cloud Run (fully managed) container instances are sandboxed using the gVisor container runtime sandbox. As documented in the syscall compatibility reference, some system calls might not be supported by this container sandbox.

Cloud Run for Anthos on Google Cloud does not use any container sandbox.

Container instance metadata server

Cloud Run container instances expose a metadata server that you can use to retrieve details about your container instance, such as the project ID, region, instance ID or service accounts. It can also be used to generate tokens for the runtime service account.

You can access this data from the metadata server using simple HTTP requests to the http://metadata.google.internal/ endpoint with the Metadata-Flavor: Google header: no client libraries are required. For more information, see Getting metadata.

The following table lists some of the available metadata server information:

Path Description
/computeMetadata/v1/project/project-id Project ID of this Cloud Run service
/computeMetadata/v1/instance/region Region of this Cloud Run service
/computeMetadata/v1/instance/id Unique identifier of the container instance (also available in logs).
/computeMetadata/v1/instance/service-accounts/default/token Generates a token for the runtime service account of this Cloud Run service

Note that Cloud Run (fully managed) does not provide details about which Google Cloud zone the container instances are running in. As a consequence, the metadata attribute /computeMetadata/v1/instance/zone always returns projects/PROJECT-NUMBER/zones/REGION-1.