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# RabbitMQ

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RabbitMQ is a messaging broker, an intermediary for messaging. It gives your applications a common platform to send and receive messages, and your messages a safe place to live until received.

## Installation

Install the rabbitmq package.

## Configuration

No configuration should be needed. Simply start and/or enable `rabbitmq.service`.

Default configuration file location `/etc/rabbitmq/rabbitmq-env.conf`. See more about configuration on the official docs

This article or section is out of date.

Reason: Plugin path changed with 4.0.5 (Discuss in Talk:RabbitMQ#Plugins Directory Missing)

### Enabling MQTT

RabbitMQ can act as MQTT server. For this functionality to work following plugin needs to be enabled:

    # rabbitmq-plugins enable rabbitmq_mqtt

RabbitMQ service needs to be restarted for this change to take effect.

Clients need to authenticate before they can post to topics. RabbitMQ segregates traffic via virtual hosts, you need to issue `configured_vhost_name:your_user_name` as user name in order to authenticate.

### Enabling HTTP admin

To enable the HTTP admin page:

    # rabbitmq-plugins enable rabbitmq_management

Then navigate to `<ip_address_of_host>:15672`. Default credentials are `username:guest password:guest`

## Troubleshooting

### Service stop hangs for a minutes

Rabbitmq package install epmd (Erlang Port Mapping Daemons) as dependency. If you run rabbitmq server via systemd, it will start detached epmd process, that will not be stopped with `systemctl stop`. You can avoid this, if add `After=epmd.service` in `[Unit]` section. Do not forget to reload daemons.

### Changed hostname

If you have changed your hostname after you installed rabbitmq, it will no longer be able to start. This is due to the `NODENAME` specified in `/etc/rabbitmq/rabbitmq-env.conf`. Update it to reflect your new hostname, for example:

    /etc/rabbitmq/rabbitmq-env.conf

    NODENAME=rabbit@my-new-hostname
    ...

### Upgraded RabbitMQ to latest version and cannot start

This might cause your `/etc/rabbitmq/rabbitmq-env.conf` to get the wrong `NODENAME`. For example, it might cause it to add another `@hostname` part. In any case, this can be fixed by following #Changed hostname.

In case the service does not start with error:

    BOOT FAILED
    [error] <0.218.0> ===========
    [error] <0.218.0> Error during startup:  {error,failed_to_initialize_feature_flags_registry}

It looks like this error is related to an incompatibility in the plugins folder after upgrade. One solution is to completely remove all trace of rabbitmq and reinstall:

    # pacman -Rn rabbitmq
    # rm -r /etc/rabbitmq
    # rm -r /var/lib/rabbitmq [May be unnecessary]
    # pacman -S rabbitmq
    # systemctl start rabbitmq.service

After restart with latest version (4.0.5-3) they may still be issue because of missing variables. In this case add:

    /etc/rabbitmq/rabbitmq-env.conf

    PLUGINS_DIR="/usr/lib/rabbitmq/plugins:/usr/lib/rabbitmq/lib/rabbitmq_server-4.0.5/plugins"
    ...

### Issues with rabbitmqctl and other command line tools

With latest version (4.0.5-3) it looks like `/usr/lib/rabbitmq/bin/` is not in `$PATH`, also see #Erlang cookie error.

### Erlang cookie error

Failure to authenticate might be caused by a wrong rabbitmq HOME setting:

    Authentication failed (rejected by the remote node), please check the Erlang cookie
    ...
    home dir: /root

Home can be set in the configuration file:

    /etc/rabbitmq/rabbitmq-env.conf

    ...
    HOME=/var/lib/rabbitmq
    ...

### can't establish TCP connection

If you see this error then make sure first entry with your host name within `/etc/hosts` contains the same IP address as specified within `/etc/rabbitmq/rabbitmq-env.conf` (this error is common if you configure rabbitmq to bind to specific interface).

### Can't connect with pika Python client through localhost

Trying to connect through localhost with pika Python client, raises an exception:

    ...
    pika.exceptions.ProbableAccessDeniedError: (541, "INTERNAL_ERROR - access to vhost '/' refused for user 'guest': vhost '/' is down")

Default configuration file `/etc/rabbitmq/rabbitmq-env.conf` of the package is:

    /etc/rabbitmq/rabbitmq-env.conf

    NODENAME=rabbit@localhost
    NODE_IP_ADDRESS=0.0.0.0
    NODE_PORT=5672

Removing the username part of `NODENAME`, and leaving the hostname of the machine (which should match the one shown in `/etc/hosts`), fixes the issue:

    /etc/rabbitmq/rabbitmq-env.conf

    NODENAME=localhost
    NODE_IP_ADDRESS=0.0.0.0
    NODE_PORT=5672

## See also

- Wikipedia:RabbitMQ
- erlang kernel parameters - kernel parameters for advanced configuration
- rabbitmq.config example - rabbitmq.config example (not included with rabbitmq package)

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