# What is RabbitMQ?

RabbitMQ is open source message broker software (sometimes called message-oriented middleware) that implements the Advanced Message Queuing Protocol (AMQP). The RabbitMQ server is written in the Erlang programming language and is built on the Open Telecom Platform framework for clustering and failover. Client libraries to interface with the broker are available for all major programming languages.

> [wikipedia.org/wiki/RabbitMQ](https://en.wikipedia.org/wiki/RabbitMQ)

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# How to use this image

## Running the daemon

One of the important things to note about RabbitMQ is that it stores data based on what it calls the "Node Name", which defaults to the hostname. What this means for usage in Docker is that we should specify `-h`/`--hostname` explicitly for each daemon so that we don't get a random hostname and can keep track of our data:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit %%IMAGE%%:3
```

This will start a RabbitMQ container listening on the default port of 5672. If you give that a minute, then do `docker logs some-rabbit`, you'll see in the output a block similar to:

	=INFO REPORT==== 6-Jul-2015::20:47:02 ===
	node           : rabbit@my-rabbit
	home dir       : /var/lib/rabbitmq
	config file(s) : /etc/rabbitmq/rabbitmq.config
	cookie hash    : UoNOcDhfxW9uoZ92wh6BjA==
	log            : tty
	sasl log       : tty
	database dir   : /var/lib/rabbitmq/mnesia/rabbit@my-rabbit

Note the `database dir` there, especially that it has my "Node Name" appended to the end for the file storage. This image makes all of `/var/lib/rabbitmq` a volume by default.

### Memory Limits

RabbitMQ contains functionality which explicitly tracks and manages memory usage, and thus needs to be made aware of cgroup-imposed limits.

The upstream configuration setting for this is `vm_memory_high_watermark`, and it is described under ["Memory Alarms"](https://www.rabbitmq.com/memory.html) in the documentation.

In this image, this value is set via `RABBITMQ_VM_MEMORY_HIGH_WATERMARK`. The value of this environment variable is interpreted as follows:

-	`0.49` is treated as `49%`, just like upstream (`{ vm_memory_high_watermark, 0.49 }`)
-	`56%` is treated as `56%` (`0.56`; `{ vm_memory_high_watermark, 0.56 }`)
-	`1073741824` is treated as an absolute number of bytes (`{ vm_memory_high_watermark, { absolute, 1073741824 } }`)
-	`1024MiB` is treated as an absolute number of bytes with a unit (`{ vm_memory_high_watermark, { absolute, "1024MiB" } }`)

The main behavioral difference is in how percentages are handled. If the current container has a memory limit (`--memory`/`-m`), a percentage value will be calculated to an absolute byte value based on the memory limit, rather than being passed to RabbitMQ as-is. For example, a container run with `--memory 2048m` (and the implied upstream-default `RABBITMQ_VM_MEMORY_HIGH_WATERMARK` of `40%`) will set the effective limit to `819MB` (which is `40%` of `2048MB`).

### Erlang Cookie

See the [RabbitMQ "Clustering Guide"](https://www.rabbitmq.com/clustering.html#erlang-cookie) for more information about cookies and why they're necessary.

For setting a consistent cookie (especially useful for clustering but also for remote/cross-container administration via `rabbitmqctl`), use `RABBITMQ_ERLANG_COOKIE`:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit -e RABBITMQ_ERLANG_COOKIE='secret cookie here' %%IMAGE%%:3
```

This can then be used from a separate instance to connect:

```console
$ docker run -it --rm --link some-rabbit:my-rabbit -e RABBITMQ_ERLANG_COOKIE='secret cookie here' %%IMAGE%%:3 bash
root@f2a2d3d27c75:/# rabbitmqctl -n rabbit@my-rabbit list_users
Listing users ...
guest   [administrator]
```

Alternatively, one can also use `RABBITMQ_NODENAME` to make repeated `rabbitmqctl` invocations simpler:

```console
$ docker run -it --rm --link some-rabbit:my-rabbit -e RABBITMQ_ERLANG_COOKIE='secret cookie here' -e RABBITMQ_NODENAME=rabbit@my-rabbit %%IMAGE%%:3 bash
root@f2a2d3d27c75:/# rabbitmqctl list_users
Listing users ...
guest   [administrator]
```

### Management Plugin

There is a second set of tags provided with the [management plugin](https://www.rabbitmq.com/management.html) installed and enabled by default, which is available on the standard management port of 15672, with the default username and password of `guest` / `guest`:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit %%IMAGE%%:3-management
```

You can access it by visiting `http://container-ip:15672` in a browser or, if you need access outside the host, on port 8080:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit -p 8080:15672 %%IMAGE%%:3-management
```

You can then go to `http://localhost:8080` or `http://host-ip:8080` in a browser.

### Setting default user and password

If you wish to change the default username and password of `guest` / `guest`, you can do so with the `RABBITMQ_DEFAULT_USER` and `RABBITMQ_DEFAULT_PASS` environmental variables:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit -e RABBITMQ_DEFAULT_USER=user -e RABBITMQ_DEFAULT_PASS=password %%IMAGE%%:3-management
```

You can then go to `http://localhost:8080` or `http://host-ip:8080` in a browser and use `user`/`password` to gain access to the management console

### Setting default vhost

If you wish to change the default vhost, you can do so with the `RABBITMQ_DEFAULT_VHOST` environmental variables:

```console
$ docker run -d --hostname my-rabbit --name some-rabbit -e RABBITMQ_DEFAULT_VHOST=my_vhost %%IMAGE%%:3-management
```

### Enabling HiPE

**Warning:** if you're using the Alpine variant, there is currently [an outstanding bug (Alpine Linux bug #5700) with the `erlang-hipe` package](https://bugs.alpinelinux.org/issues/5700) which prevents HiPE from working in Alpine Linux. See [docker-library/rabbitmq#151](https://github.com/docker-library/rabbitmq/issues/151) for more discussion.

See the [RabbitMQ "Configuration"](http://www.rabbitmq.com/configure.html#config-items) for more information about various configuration options.

For enabling the HiPE compiler on startup use `RABBITMQ_HIPE_COMPILE` set to `1`. Accroding to the official documentation:

> Set to true to precompile parts of RabbitMQ with HiPE, a just-in-time compiler for Erlang. This will increase server throughput at the cost of increased startup time. You might see 20-50% better performance at the cost of a few minutes delay at startup.

It is therefore important to take that startup delay into consideration when configuring health checks, automated clustering etc.

### Additional Configuration

If additional configuration is required, it is recommended to use the `RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS` environment variable, whose syntax is described [in section 7.8 ("Configuring an Application") of the Erlang OTP Design Principles User's Guide](http://erlang.org/doc/design_principles/applications.html#id81887) (the appropriate value for `-ApplName` is `-rabbit`).

For example, configuring [`log_levels`](https://www.rabbitmq.com/configure.html#config-items) would look something like `-e RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-rabbit log_levels [{connection,error}]"`.

Additional configuration keys would be specified as a list. For example, configuring both [`log_levels`](https://www.rabbitmq.com/configure.html#config-items) and [`auth_backends`](https://www.rabbitmq.com/ldap.html#overview) would look something like `-e RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS="-rabbit log_levels [{connection,error}] auth_backends [rabbit_auth_backend_ldap]"`.

## Connecting to the daemon

```console
$ docker run --name some-app --link some-rabbit:rabbit -d application-that-uses-rabbitmq
```