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1. Check whether LocalStack started and is healthy
First determine whether LocalStack is running at all. If you launched it with lstk, run lstk status. For a Docker-based deployment, run docker ps -a and check whether the container is running or has exited. After its initial health-starting period, a healthy container should show Up (healthy). LocalStack’s installation guide describes these startup checks.
Then test whether the gateway responds from the same host:
curl http://localhost:4566/_localstack/healthA health response confirms that the gateway is reachable at that address. It reports the LocalStack edition, version, and service states; individual services may show as available before you have used them.
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If the runtime is unavailable
If lstk status reports runtime not healthy, start or repair the container runtime before troubleshooting LocalStack itself. The lstk FAQ and troubleshooting guide lists Docker Desktop, Rancher Desktop, Colima, OrbStack, Lima, and Podman as supported runtime options. How to start the runtime depends on your host and which option you use.
If the container exits or stays unhealthy
Read the complete startup log rather than only the last error line:
docker logs <container-id>Look for the first warning or error before the exit code or final traceback. LocalStack’s FAQ also recommends checking outbound HTTPS and DNS access for documented startup issues. Its suggested host-side checks include curl -v https://api.localstack.cloud/v1/health and a DNS lookup of api.localstack.cloud. These are diagnostics, not proof that every failed startup has the same cause.
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2. Check port 4566, listener settings, and port conflicts
Port 4566 is LocalStack’s main edge/API gateway. A process can be running while a client still cannot reach it if the gateway is not listening on the expected interface or Docker has not published the port. Check the actual mappings with docker ps and compare them with the listener configuration. The configuration reference documents the listener settings; the installation guide covers Docker-based access.
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In Docker mode, the documented default GATEWAY_LISTEN is 0.0.0.0:4566,0.0.0.0:443. In host mode, the defaults bind to loopback. Docker Compose and docker run deployments need the appropriate port publication for host access. For example, a container’s internal listener alone does not make that port reachable from the host unless it is published.
When port 443 is already in use
A 443 conflict does not always prevent lstk from starting. Its FAQ says the default 443 publication can be dropped while the edge service continues on 4566. If you do not need the 443 listener, configure GATEWAY_LISTEN for only 0.0.0.0:4566.
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That fallback does not apply to every port conflict: a port explicitly required by a custom GATEWAY_LISTEN is a hard requirement and can prevent startup. Distinguish a conflict on the default 443 publication from a conflict on a port your own configuration requires, then verify the ports that were actually published.
3. Use an address that works from the client’s network
The correct endpoint depends on where the AWS CLI or SDK runs. The same localhost:4566 string does not work unchanged in every setup because localhost refers to the machine or container making the request.
| Client location | Addressing approach | What to check |
|---|---|---|
| On the same host as LocalStack | Use localhost:4566 or a hostname that resolves to the host’s loopback address. |
Publish port 4566 from Docker and confirm the gateway health URL responds from that host. |
| In a sibling container | Connect the client and LocalStack containers to a shared Docker network; use the LocalStack service or container name and port. | localhost points to the client container itself, not LocalStack. |
| On another host | Listen on a reachable interface, such as 0.0.0.0, publish the port, and use an address reachable from that host. |
Apply the network’s access controls; a loopback-only listener is not reachable remotely. |
| Inside a LocalStack-created container | Use the address and networking arrangement appropriate to that container’s network. | Do not assume the host’s loopback address is reachable from the container. |
LocalStack’s endpoint URL guide explains the access patterns. Its networking overview states: “LocalStack only binds to IPv4 addresses (e.g. 127.0.0.1).” If the service appears healthy but the client cannot connect, check whether the client is attempting IPv6 while LocalStack is listening on IPv4.
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4. Point the AWS SDK or CLI at LocalStack
AWS SDKs do not automatically send requests to LocalStack in the ordinary explicit-endpoint setup. Configure the SDK’s endpoint setting, profile, or supported environment variable. LocalStack’s AWS SDK overview gives language-specific instructions for .NET, C++, Go, Java, JavaScript, PHP, Python/Boto3, and Ruby.
Common endpoint forms are http://localhost:4566 and http://localhost.localstack.cloud:4566. Choose one that resolves and routes correctly from the client’s network location; neither is universal for host, container, and remote clients.
For AWS CLI on the host
Pass the LocalStack URL with --endpoint-url. The official AWS CLI guide uses these example local-development settings:
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export AWS_ACCESS_KEY_ID=test
export AWS_SECRET_ACCESS_KEY=test
export AWS_DEFAULT_REGION=us-east-1
aws --endpoint-url=http://localhost.localstack.cloud:4566 <service-command>These credentials and region are example local-development values, not production AWS credentials. Replace <service-command> with the AWS CLI operation you want to run.
For AWS CLI or SDK in a container
If the CLI runs in its own container, the host’s published localhost:4566 is not automatically its LocalStack address. Put both containers on a shared Docker network and use the LocalStack service or container name as the hostname, following the networking example in the AWS CLI guide.
5. Fix an x509 certificate hostname mismatch
An error saying a certificate is valid for a LocalStack hostname but not an amazonaws.com hostname can indicate that the client is requesting an AWS hostname while its traffic is being routed to LocalStack. The LocalStack FAQ recommends explicitly setting the LocalStack endpoint for this case and prefers HTTP for local development.
Set an endpoint such as AWS_ENDPOINT_URL=http://localhost:4566 or AWS_ENDPOINT_URL=http://localhost.localstack.cloud:4566, adjusted for the client’s network. Do not broadly disable certificate validation to work around a hostname mismatch. Transparent endpoint injection has separate DNS and TLS requirements; use its dedicated documentation rather than applying the ordinary explicit-endpoint fix.
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If the checks above do not explain the failure, record the information that distinguishes a startup problem from a routing or client configuration problem:
- How LocalStack was launched and its version.
- The runtime status and whether the container is running, healthy, or exited.
- The complete port mapping and configured listener.
- Where the client runs: on the host, in a sibling container, in a LocalStack-created container, or on another host.
- The exact endpoint hostname, port, and protocol configured in the client.
- The response from
http://localhost:4566/_localstack/healthwhen tested from the relevant host. - The complete startup logs, including lines before the final error.
The FAQ documents a diagnose endpoint that can generate a compressed diagnostic bundle when LocalStack serves HTTP and debug mode is enabled. LocalStack describes the output as extensive and potentially sensitive, so review and handle it carefully before sharing.
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