RabbitMQ Configuration

Reference documentation

What is RabbitMQ?

RabbitMQ is a message bus, which describes itself as “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”.

To learn more about RabbitmQ, please visit the official RabbitMQ website.

How does Sensu use RabbitMQ?

Sensu services use RabbitMQ (the default Sensu transport) to communicate with one another. Every Sensu service requires access to the same instance of RabbitMQ or a RabbitMQ cluster to function. Sensu check requests and check results are sent over RabbitMQ to the approprate Sensu services.

Install RabbitMQ

For more information about installing RabbitMQ for use with Sensu, please visit the RabbitMQ installation guide.

Configure Sensu

Example configurations

The following are an example RabbitMQ connection definitions, each located at /etc/sensu/conf.d/rabbitmq.json.

Example standalone configuration

{
  "rabbitmq": {
    "host": "127.0.0.1",
    "port": 5671,
    "vhost": "/sensu",
    "user": "sensu",
    "password": "secret",
    "heartbeat": 30,
    "prefetch": 50,
    "ssl": {
      "cert_chain_file": "/etc/sensu/ssl/cert.pem",
      "private_key_file": "/etc/sensu/ssl/key.pem"
    }
  }
}

Example distributed configuration

{
  "rabbitmq": {
    "host": "10.0.1.6",
    "port": 5671,
    "vhost": "/sensu",
    "user": "sensu",
    "password": "secret",
    "heartbeat": 30,
    "prefetch": 50,
    "ssl": {
      "cert_chain_file": "/etc/sensu/ssl/cert.pem",
      "private_key_file": "/etc/sensu/ssl/key.pem"
    }
  }
}

Example high-availability configuration

{
  "rabbitmq": [
    {
      "host": "10.0.0.6",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    },
    {
      "host": "10.0.0.7",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    },
    {
      "host": "10.0.0.8",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    }
  ]
}

RabbitMQ definition specification

The RabbitMQ definition uses the "rabbitmq": {} definition scope.

rabbitmq attributes

host
description
The RabbitMQ hostname or IP address (recommended).
required
false
type
String
default
127.0.0.1
example
"host": "8.8.8.8"
port
description
The RabbitMQ TCP port.
required
false
type
Integer
default
5672
example
"port": 5671
vhost
description
The RabbitMQ vhost to use.
required
false
type
String
default
/
example
"vhost": "/sensu"
user
description
The RabbitMQ user name.
required
false
type
String
default
guest
example
"user": "sensu"
password
description
The RabbitMQ user password.
required
false
type
String
default
guest
example
"password": "secret"
heartbeat
description
The RabbitMQ AMQP connection heartbeat in seconds. Enabling can help in early detection of disrupted TCP connections causing the RabbitMQ client to attempt re-connection to the server much earlier than if left disabled. _NOTE: if this setting is not defined or set to 0 then RabbitMQ client heartbeats are disabled.
required
false
type
Integer
example
"heartbeat": 30
prefetch
description
The RabbitMQ AMQP consumer prefetch value, setting the number of unacknowledged messages allowed for the channel. This attribute can be used as a flow control mechanism, to tune message throughput performance. NOTE: an increased prefetch value should be used if you are experiencing a backlog of messages in RabbitMQ while the Sensu server(s) load remains low. Increasing the prefetch value will effect the distribution of messages in Sensu configurations with more than one Sensu server.
required
false
type
Integer
default
1
example
"prefetch": 100
ssl
description
A set of attributes that configure SSL encryption for the connection. SSL encryption will be enabled if this attribute is configured.
required
false
type
Hash
example
"ssl": {}

ssl attributes

The following attributes are configured within the "ssl": {} RabbitMQ definition attribute scope.

cert_chain_file
description
The file path for the chain of X509 SSL certificates in the PEM format for the SSL connection.
required
true
type
String
example
"cert_chain_file": "/etc/sensu/ssl/cert.pem"
private_key_file
description
The file path for the SSL private key in the PEM format.
required
true
type
String
example
"private_key_file": "/etc/sensu/ssl/key.pem"

Configure RabbitMQ

To configure RabbitMQ, please refer to the official RabbitMQ configuration documentation.

Standalone configuration

For standalone configurations, no additional configuration changes are required beyond what is documented in the RabbitMQ installation guide.

Distributed configuration

For distributed configurations (e.g. where RabbitMQ is running on dedicated systems), RabbitMQ may need to be configure to listen for connections from external systems using the tcp_listeners configuration directive.

To enable support for external connections, please ensure that your /etc/rabbitmq/rabbitmq.config file contains the following configuration snippet:

[
  {rabbit, [
    {tcp_listeners, [{"0.0.0.0", 5672}]}
  ]}
].

High-availability configuration

What is a RabbitMQ cluster?

RabbitMQ supports grouping of several RabbitMQ servers into a cluster. The official RabbitMQ clustering documentation describes clusters as follows:

A RabbitMQ broker is a logical grouping of one or several Erlang nodes, each running the RabbitMQ application and sharing users, virtual hosts, queues, exchanges, bindings, and runtime parameters. Sometimes we refer to the collection of nodes as a cluster.

In high availability configurations, all of the Sensu processes need to be able to communicate with a member of a single RabbitMQ cluster.

High-availability hardware requirements

The Sensu transport does not require message persistence, making throughput the primary concern for RabbitMQ (i.e. memory is more important than disk performance). When starting with a RabbitMQ cluster it is important to use systems with sufficient compute, memory, and network resources. Although it’s challenging to provide “recommended hardware requirements” for every possible Sensu installation, we have found that starting with three nodes equivalent to AWS EC2 m3.medium instances generally provides a solid baseline for monitoring 1000+ servers, each reporting 10-20 checks (& metrics) at a 10-second interval.

For the best results when configuring RabbitMQ for high availability applications, we recommend a three (3) node RabbitMQ cluster, as running fewer or more nodes introduces additional failure modes.

Install RabbitMQ

Before configuring a RabbitMQ cluster, RabbitMQ must be installed on all of the systems you will use to provide the RabbitMQ services. For RabbitMQ installation instructions, please refer to the Sensu RabbitMQ installation guide. Once RabbitMQ has been installed and started, you may proceed to configure the RabbitMQ cluster.

Configure a RabbitMQ cluster

While much of the configuration for RabbitMQ lives in a configuration file located at /etc/rabbitmq/rabbitmq.config, some things do not mesh well with the use of a configuration file. RabbitMQ calls these items “runtime parameters and policies”, which are defined using the rabbitmqctl utility. For more information on configuring RabbitMQ, please visit the official RabbitMQ configuration documentation.

To configure your three node RabbitMQ cluster for use with Sensu, please note the following instructions:

  1. Stop the RabbitMQ service on all three RabbitMQ systems.

    NOTE: The service command will not work on CentOS 5, the sysvinit script must be used, e.g. sudo /etc/init.d/rabbitmq-server stop

    sudo service rabbitmq-server stop
    
  2. Enable RabbitMQ pause_minority network partition handling. Please ensure that your /etc/rabbitmq/rabbitmq.config configuration file contains the following configuration snippet:

    [
      {rabbit, [
        {cluster_partition_handling, pause_minority}
      ]}
    ].
    

    NOTE: a RabbitMQ cluster offers several methods of handling network partitions. A RabbitMQ cluster should not span regions (e.g. WAN links), as doing so would increase latency and the probability of network partitions.

  3. Set the RabbitMQ erlang cookie on all 3 selected instances to the same value (e.g. cookiemonster). Create and/or edit the file located at /var/lib/rabbitmq/.erlang.cookie so that it contains the following contents:

    coookiemonster
    

    WARNING: if this file is edited while RabbitMQ is running it may prevent the RabbitMQ process from stopping and/or restarting gracefully, which is why step #1 of these instructions indicates that the RabbitMQ services should be stopped before making configuration changes.

  4. Start RabbitMQ on all three RabbitMQ systems.

    NOTE: The service command will not work on CentOS 5, the sysvinit script must be used, e.g. sudo /etc/init.d/rabbitmq-server start

    sudo service rabbitmq-server start
    
  5. Reset the RabbitMQ nodes on all 3 selected instances in preparation for clustering.

    sudo rabbitmqctl stop_app
    sudo rabbitmqctl reset
    
  6. Start the RabbitMQ application on one of the three RabbitMQ systems, and obtain the IP address of this system for instructing the remaining systems on where to join the RabbitMQ cluster.

    sudo rabbitmqctl start_app
    ifconfig
    

    NOTE: this step effectively starts the RabbitMQ “cluster”, which the other RabbitMQ systems will join in the following steps. for the purposes of this guide we will assume 10.0.1.6 is the IP address of this system.

  7. Join the other two RabbitMQ systems to the RabbitMQ cluster started in step #6 using the rabbitmqctl utility, and the IP address obtained in step #6.

    sudo rabbitmqctl join_cluster rabbit@ip-10-0-1-6
    sudo rabbitmqctl start_app
    

    NOTE: these commands need to be run twice - once on each of the remaining two RabbitMQ systems in the cluster.

    WARNING: when adding a RabbitMQ broker to a cluster (e.g. rabbitmqctl join_cluster rabbit@hostname, the brokers must be able to successfully resolve each other’s hostname.

  8. Add the Sensu vhost and user credentials from any system in the new RabbitMQ cluster.

    sudo rabbitmqctl add_vhost /sensu
    sudo rabbitmqctl add_user sensu secret
    sudo rabbitmqctl set_permissions -p /sensu sensu ".*" ".*" ".*"
    sudo rabbitmqctl list_permissions -p /sensu
    

    NOTE: please replace secret with your desired password. These vhost and user credentials will be automatically replicated to the other instances in the RabbitMQ cluster.

  9. Create a RabbitMQ policy to enable high-availability for Sensu’s result and keepalive queues:

    sudo rabbitmqctl set_policy ha-sensu "^(results$|keepalives$)" '{"ha-mode":"all", "ha-sync-mode":"automatic"}' -p /sensu
    sudo rabbitmqctl list_policies -p /sensu
    

    NOTE: by default, queues within a RabbitMQ cluster are located on a single node (the node on which they were first declared). This is in contrast to exchanges and bindings, which can always be considered to be on all nodes in a RabbitMQ cluster. Sensu requires specific queues to be mirrored across all RabbitMQ nodes in a RabbitMQ cluster. The Sensu results and keepalives queues MUST be mirrored. Sensu client subscription queues do not need to be mirrored.

    WARNING: RabbitMQ uses policies to determine which queues are mirrored. The command provided above will create a RabbitMQ policy to mirror the Sensu results and keealives queues in the RabbitMQ vhost named /sensu. If you have modified your configuration to use a vhost other than /sensu, please proceed accordingly.

Configure Sensu to use the RabbitMQ cluster

Sensu services (e.g. sensu-client) can be configured with the connection information for each RabbitMQ node in a RabbitMQ cluster without the need for load-balancing middleware (e.g. HAProxy). Sensu will randomly sort the configured RabbitMQ connections and attempt to connect to one of the nodes in the cluster. If Sensu is unable to connect to a node in a RabbitMQ cluster, or if Sensu loses connectivity to a node in a RabbitMQ cluster, it will attempt to connect (or reconnect) to the next node in the RabbitMQ cluster.

To configure Sensu to connect to a RabbitMQ cluster, the "rabbitmq" configuration Hash can be replaced with an Array of RabbitMQ connection configurations (i.e. "rabbitmq": [] instead of "rabbitmq": {}).

The following is an example RabbitMQ definition that configures Sensu to connect to a RabbitMQ cluster.

NOTE: the RabbitMQ nodes must first be successfully clustered in order for Sensu to operate.

{
  "rabbitmq": [
    {
      "host": "10.0.0.1",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    },
    {
      "host": "10.0.0.2",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    },
    {
      "host": "10.0.0.3",
      "port": 5671,
      "vhost": "/sensu",
      "user": "sensu",
      "password": "secret",
      "heartbeat": 30,
      "prefetch": 50,
      "ssl": {
        "cert_chain_file": "/etc/sensu/ssl/cert.pem",
        "private_key_file": "/etc/sensu/ssl/key.pem"
      }
    }
  ]
}

Securing RabbitMQ

Sensu leverages RabbitMQ access control and SSL for secure communication. Sensu was created to deal with dynamic infrastructure, where it is not feasible to maintain strict firewall rules. It is common to expose RabbitMQ’s SSL port (5671) without any restrictions, if certain conditions are met. Removing the default RabbitMQ user guest is mandatory and using a generated user name, password, and vhost is highly recommended. Enabling SSL peer certificate verification will ensure only trusted RabbitMQ clients with the correct private key are able to connect.

RabbitMQ and SELinux

If SELinux is enabled on the machine(s) reponsible for running RabbitMQ, you may need to make minor policy changes in order for RabbitMQ (and Erlang) to run successfully.

To list the available SELinux booleans, run the following command:

sudo getsebool -a

For some reason, enabling the NIS boolean allows RabbitMQ to bind to its TCP socket and operate normally.

sudo setsebool -P nis_enabled 1

RabbitMQ SSL

For more information on configuring RabbitMQ to use SSL, please visit the Sensu SSL documentation.

RabbitMQ SSL and Erlang 18.3

For users of Erlang version 18.3, the SSL implementation that RabbitMQ relies on changed in such a way that additional configuration parameters are needed for SSL encrypted communication between Sensu and RabbitMQ (specifically affecting Sensu Enterprise users). This does not apply to Erlang 19.0+

In order to enable SSL communication between RabbitMQ installations running on Erlang 18.3 and Sensu, it is necessary to configure the specific TLS version (i.e. {versions, ['tlsv1.2']}) and ciphers (i.e. {ciphers, [{rsa,aes_256_cbc,sha256}]}) that RabbitMQ will accept, and to reject clients with no certificate (i.e. {fail_if_no_peer_cert,true}).

[
 {rabbit, [
    {ssl_listeners, [5671]},
    {ssl_options, [{cacertfile,"/etc/rabbitmq/ssl/cacert.pem"},
                   {certfile,"/etc/rabbitmq/ssl/cert.pem"},
                   {keyfile,"/etc/rabbitmq/ssl/key.pem"},
                   {versions, ['tlsv1.2']},
                   {ciphers,  [{rsa,aes_256_cbc,sha256}]},
                   {verify,verify_peer},
                   {fail_if_no_peer_cert,true}]}
  ]}
].

WARNING: if you are seeing RabbitMQ log entries with messages like Fatal error: insufficient security, and using Erlang 18.3, please confirm that the above stated configuration changes are in place.

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