> ## Documentation Index
> Fetch the complete documentation index at: https://www.aptible.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Containers

Aptible deploys all resources in Containers.

# Container Command

Containers run the command specified by the [Service](/core-concepts/apps/deploying-apps/services) they belong to:

* If the service is an [Implicit Service](/how-to-guides/app-guides/define-services#implicit-service-cmd), then that command is the [Image](/core-concepts/apps/deploying-apps/image/overview)'s `CMD`.
* If the service is an [Explicit Service](/how-to-guides/app-guides/define-services#explicit-services-procfiles), then that command is defined by the [Procfile](/how-to-guides/app-guides/define-services).

# Container Environment

Containers run with three types of environment variables and if there is a name collision, [Aptible Metadata](/reference/aptible-metadata-variables) takes precedence over App Configuration, which takes precedence over Docker Image Variables:

## Docker Image Variables

Docker [Images](/core-concepts/apps/deploying-apps/image/overview) define these variables via the `ENV` directive. They are present when your Containers start:

```dockerfile theme={null}
ENV FOO=BAR
```

## App Configuration

Aptible injects an App's [Configuration](/core-concepts/apps/deploying-apps/configuration) as environment variables. For example, for the keys `FOO` and `BAR`:

```shell theme={null}
aptible config:set --app "$APP_HANDLE" \
  FOO=SOME BAR=OTHER
```

Aptible runs containers with the environment variables `FOO` and `BAR` set respectively to `SOME` and `OTHER`.

## Aptible Metadata

Finally, Aptible injects a set of [metadata keys](/reference/aptible-metadata-variables) as environment variables.

These environment variables are accessible through the facilities exposed by the language, such as `ENV` in Ruby, `process.env` in Node, or `os.environ` in Python.

# Container Hostname

Aptible (and Docker in general) sets the hostname for your Containers to the 12 first characters of the Container's ID and uses it in [Logging](/core-concepts/observability/logs/overview) and [Metrics](/core-concepts/observability/metrics/overview).

# Container Isolation

Containers on Aptible are isolated. Use one of the following options to allow multiple Containers to communicate:

* For web APIs or microservices, set up an [Endpoint](/core-concepts/apps/connecting-to-apps/app-endpoints/overview) and direct your requests to the Endpoint.
* For background workers, use a [Database](/core-concepts/managed-databases/overview) as a message queue. Aptible supports [Redis](/core-concepts/managed-databases/supported-databases/redis) and [RabbitMQ](/core-concepts/managed-databases/supported-databases/rabbitmq), which are well-suited for this use case.

# Container Lifecycle

Containers on Aptible are frequently recycled during Operations - meaning new Containers are created during an Operation, and the old ones are terminated. This happens within the following Operations:

* Redeploying an App
* Restarting an App or Database
* Scaling an App or Database

### Graceful termination

Containers are given a grace period after the initial `SIGTERM` to exit before receiving a hard `SIGKILL`. By default this is 10 seconds, but it can be configured via the **stop timeout** setting on the service. See the [Releases](/core-concepts/apps/deploying-apps/releases/overview) page for more information and caveats.

# Filesystem Implications

By default, the filesystem for your [Containers](/core-concepts/architecture/containers/overview) is ephemeral, with the notable exceptions of [Database](/core-concepts/managed-databases/overview) data and any [Persistent Disk](/core-concepts/apps/persistent-disks) attached to an App service. Any data stored on the ephemeral filesystem will be gone every time containers are recycled.

For most workloads, do not use the filesystem to retain long-term data. Instead, store data in a Database or a third-party storage solution, such as AWS S3 (see [How do I accept file uploads when using Aptible?](/how-to-guides/app-guides/use-s3-to-accept-file-uploads) for more information). For workloads that need durable local state and don't fit into a Managed Database, see [Persistent Disks](/core-concepts/apps/persistent-disks).

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