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LocalStack

Since testcontainers-go v0.18.0

Introduction

The Testcontainers module for LocalStack is "a fully functional local AWS cloud stack", to develop and test your cloud and serverless apps without actually using the cloud.

Adding this module to your project dependencies

Please run the following command to add the LocalStack module to your Go dependencies:

go get github.com/testcontainers/testcontainers-go/modules/localstack

Usage example

Running LocalStack as a stand-in for multiple AWS services during a test:

ctx := context.Background()

localstackContainer, err := localstack.RunContainer(ctx,
    testcontainers.WithImage("localstack/localstack:1.4.0"),
)
if err != nil {
    panic(err)
}

// Clean up the container
defer func() {
    if err := localstackContainer.Terminate(ctx); err != nil {
        panic(err)
    }
}()

Environment variables listed in Localstack's README may be used to customize Localstack's configuration. Use the OverrideContainerRequest option when creating the LocalStackContainer to apply configuration settings.

Module reference

The LocalStack module exposes one single function to create the LocalStack container, and this function receives two parameters:

func RunContainer(ctx context.Context, opts ...testcontainers.ContainerCustomizer) (*LocalStackContainer, error)
  • context.Context, the Go context.
  • testcontainers.ContainerCustomizer, a variadic argument for passing options.

Container Options

When starting the Localstack container, you can pass options in a variadic way to configure it.

Image

By default, the image used is localstack:1.4.0. If you need to use a different image, you can use testcontainers.WithImage option.

Image Substitutions

In more locked down / secured environments, it can be problematic to pull images from Docker Hub and run them without additional precautions.

An image name substitutor converts a Docker image name, as may be specified in code, to an alternative name. This is intended to provide a way to override image names, for example to enforce pulling of images from a private registry.

Testcontainers for Go exposes an interface to perform this operations: ImageSubstitutor, and a No-operation implementation to be used as reference for custom implementations:

// ImageSubstitutor represents a way to substitute container image names
type ImageSubstitutor interface {
    // Description returns the name of the type and a short description of how it modifies the image.
    // Useful to be printed in logs
    Description() string
    Substitute(image string) (string, error)
}

type NoopImageSubstitutor struct{}

// Description returns a description of what is expected from this Substitutor,
// which is used in logs.
func (s NoopImageSubstitutor) Description() string {
    return "NoopImageSubstitutor (noop)"
}

// Substitute returns the original image, without any change
func (s NoopImageSubstitutor) Substitute(image string) (string, error) {
    return image, nil
}

Using the WithImageSubstitutors options, you could define your own substitutions to the container images. E.g. adding a prefix to the images so that they can be pulled from a Docker registry other than Docker Hub. This is the usual mechanism for using Docker image proxies, caches, etc.

Wait Strategies

If you need to set a different wait strategy for the container, you can use testcontainers.WithWaitStrategy with a valid wait strategy.

Info

The default deadline for the wait strategy is 60 seconds.

At the same time, it's possible to set a wait strategy and a custom deadline with testcontainers.WithWaitStrategyAndDeadline.

Startup Commands

Testcontainers exposes the WithStartupCommand(e ...Executable) option to run arbitrary commands in the container right after it's started.

Info

To better understand how this feature works, please read the Create containers: Lifecycle Hooks documentation.

It also exports an Executable interface, defining one single method: AsCommand(), which returns a slice of strings to represent the command and positional arguments to be executed in the container.

You could use this feature to run a custom script, or to run a command that is not supported by the module right after the container is started.

Docker type modifiers

If you need an advanced configuration for the container, you can leverage the following Docker type modifiers:

  • testcontainers.WithConfigModifier
  • testcontainers.WithHostConfigModifier
  • testcontainers.WithEndpointSettingsModifier

Please read the Create containers: Advanced Settings documentation for more information.

Customize the container request

It's possible to entirely override the default LocalStack container request:

networkName := "localstack-network-v2"

localstack, err := RunContainer(
    ctx,
    WithNetwork(networkName, "localstack"),
    testcontainers.CustomizeRequest(testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Image: "localstack/localstack:2.0.0",
            Env:   map[string]string{"SERVICES": "s3,sqs"},
        },
    }),
)

With simply passing the testcontainers.CustomizeRequest functional option to the RunContainer function, you'll be able to configure the LocalStack container with your own needs, as this new container request will be merged with the original one.

In the above example you can check how it's possible to set certain environment variables that are needed by the tests, the most important ones are the AWS services you want to use. Besides, the container runs in a separate Docker network with an alias.

WithNetwork

By default, the LocalStack container is started in the default Docker network. If you want to use a different Docker network, you can use the WithNetwork(networkName string, alias string) option, which receives the new network name and an alias as parameters, creating the new network, attaching the container to it, and setting the network alias for that network.

Accessing hostname-sensitive services

Some Localstack APIs, such as SQS, require the container to be aware of the hostname that it is accessible on - for example, for construction of queue URLs in responses.

Testcontainers will inform Localstack of the best hostname automatically, using the an environment variable for that:

  • for Localstack versions 0.10.0 and above, the HOSTNAME_EXTERNAL environment variable will be set to hostname in the container request.
  • for Localstack versions 2.0.0 and above, the LOCALSTACK_HOST environment variable will be set to the hostname in the container request.

Once the variable is set:

  • when running the Localstack container directly without a custom network defined, it is expected that all calls to the container will be from the test host. As such, the container address will be used (typically localhost or the address where the Docker daemon is running).

  • when running the Localstack container with a custom network defined, it is expected that all calls to the container will be from other containers on that network. HOSTNAME_EXTERNAL will be set to the last network alias that has been configured for the Localstack container.

    ctx := context.Background()

nwName := "localstack-network"

_, err := testcontainers.GenericNetwork(ctx, testcontainers.GenericNetworkRequest{
    NetworkRequest: testcontainers.NetworkRequest{
        Name: nwName,
    },
})
if err != nil {
    panic(err)
}

localstackContainer, err := localstack.RunContainer(
    ctx,
    testcontainers.CustomizeRequest(testcontainers.GenericContainerRequest{
        ContainerRequest: testcontainers.ContainerRequest{
            Image:          "localstack/localstack:0.13.0",
            Env:            map[string]string{"SERVICES": "s3,sqs"},
            Networks:       []string{nwName},
            NetworkAliases: map[string][]string{nwName: {"localstack"}},
        },
    }),
)
if err != nil {
    panic(err)
}

  • Other usage scenarios, such as where the Localstack container is used from both the test host and containers on a custom network, are not automatically supported. If you have this use case, you should set HOSTNAME_EXTERNAL manually.

Obtaining a client using the AWS SDK for Go

You can use the AWS SDK for Go to create a client for the LocalStack container. The following examples show how to create a client for the S3 service, using both the SDK v1 and v2.

Using the AWS SDK v1

// awsSession returns a new AWS session for the given service. To retrieve the specific AWS service client, use the
// session's client method, e.g. s3manager.NewUploader(session).
func awsSession(ctx context.Context, l *localstack.LocalStackContainer) (*session.Session, error) {
    mappedPort, err := l.MappedPort(ctx, nat.Port("4566/tcp"))
    if err != nil {
        return &session.Session{}, err
    }

    provider, err := testcontainers.NewDockerProvider()
    if err != nil {
        return &session.Session{}, err
    }
    defer provider.Close()

    host, err := provider.DaemonHost(ctx)
    if err != nil {
        return &session.Session{}, err
    }

    awsConfig := &aws.Config{
        Region:                        aws.String(region),
        CredentialsChainVerboseErrors: aws.Bool(true),
        Credentials:                   credentials.NewStaticCredentials(accesskey, secretkey, token),
        S3ForcePathStyle:              aws.Bool(true),
        Endpoint:                      aws.String(fmt.Sprintf("http://%s:%d", host, mappedPort.Int())),
    }

    return session.NewSession(awsConfig)
}

For further reference on the SDK v1, please check out the AWS docs here.

Using the AWS SDK v2

func s3Client(ctx context.Context, l *localstack.LocalStackContainer) (*s3.Client, error) {
    mappedPort, err := l.MappedPort(ctx, nat.Port("4566/tcp"))
    if err != nil {
        return nil, err
    }

    provider, err := testcontainers.NewDockerProvider()
    if err != nil {
        return nil, err
    }
    defer provider.Close()

    host, err := provider.DaemonHost(ctx)
    if err != nil {
        return nil, err
    }

    customResolver := aws.EndpointResolverWithOptionsFunc(
        func(service, region string, opts ...interface{}) (aws.Endpoint, error) {
            return aws.Endpoint{
                PartitionID:   "aws",
                URL:           fmt.Sprintf("http://%s:%d", host, mappedPort.Int()),
                SigningRegion: region,
            }, nil
        })

    awsCfg, err := config.LoadDefaultConfig(context.TODO(),
        config.WithRegion(region),
        config.WithEndpointResolverWithOptions(customResolver),
        config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(accesskey, secretkey, token)),
    )
    if err != nil {
        return nil, err
    }

    client := s3.NewFromConfig(awsCfg, func(o *s3.Options) {
        o.UsePathStyle = true
    })

    return client, nil
}

For further reference on the SDK v2, please check out the AWS docs here

Testing the module

The module includes unit and integration tests that can be run from its source code. To run the tests please execute the following command:

cd modules/localstack
make test

Info

At this moment, the tests for the module include tests for the S3 service, only. They live in two different Go packages of the LocalStack module, v1 and v2, where it'll be easier to add more examples for the rest of services.