RabbitMQ is a message broker written in Erlang. It is currently the default provider of message queues in Kolla Ansible deployments.

TLS encryption

There are a number of channels to consider when securing RabbitMQ communication. Kolla Ansible currently supports TLS encryption of the following:

  • client-server traffic, typically between OpenStack services using the oslo.messaging library and RabbitMQ

  • RabbitMQ Management API and UI (frontend connection to HAProxy only)

Encryption of the following channels is not currently supported:

  • RabbitMQ cluster traffic between RabbitMQ server nodes

  • RabbitMQ CLI communication with RabbitMQ server nodes

  • RabbitMQ Management API and UI (backend connection from HAProxy to RabbitMQ)


Encryption of client-server traffic is enabled by setting rabbitmq_enable_tls to true. Additionally, certificates and keys must be available in the following paths (in priority order):


  • "{{ kolla_certificates_dir }}/{{ inventory_hostname }}/rabbitmq-cert.pem"

  • "{{ kolla_certificates_dir }}/{{ inventory_hostname }}-cert.pem"

  • "{{ kolla_certificates_dir }}/rabbitmq-cert.pem"


  • "{{ kolla_certificates_dir }}/{{ inventory_hostname }}/rabbitmq-key.pem"

  • "{{ kolla_certificates_dir }}/{{ inventory_hostname }}-key.pem"

  • "{{ kolla_certificates_dir }}/rabbitmq-key.pem"

The default for kolla_certificates_dir is /etc/kolla/certificates.

The certificates must be valid for the IP address of the host running RabbitMQ on the API network.

Additional TLS configuration options may be passed to RabbitMQ via rabbitmq_tls_options. This should be a dict, and the keys will be prefixed with ssl_options.. For example:

  ciphers.1: ECDHE-ECDSA-AES256-GCM-SHA384
  ciphers.2: ECDHE-RSA-AES256-GCM-SHA384
  ciphers.3: ECDHE-ECDSA-AES256-SHA384
  honor_cipher_order: true
  honor_ecc_order: true

Details on configuration of RabbitMQ for TLS can be found in the RabbitMQ documentation.

When om_rabbitmq_enable_tls is true (it defaults to the value of rabbitmq_enable_tls), applicable OpenStack services will be configured to use oslo.messaging with TLS enabled. The CA certificate is configured via om_rabbitmq_cacert (it defaults to rabbitmq_cacert, which points to the system’s trusted CA certificate bundle for TLS). Note that there is currently no support for using client certificates.

For testing purposes, Kolla Ansible provides the kolla-ansible certificates command, which will generate self-signed certificates for RabbitMQ if rabbitmq_enable_tls is true.

Management API and UI

The management API and UI are accessed via HAProxy, exposed only on the internal VIP. As such, traffic to this endpoint is encrypted when kolla_enable_tls_internal is true. See TLS Configuration.

Passing arguments to RabbitMQ server’s Erlang VM

Erlang programs run in an Erlang VM (virtual machine) and use the Erlang runtime. The Erlang VM can be configured.

Kolla Ansible makes it possible to pass arguments to the Erlang VM via the usage of the rabbitmq_server_additional_erl_args variable. The contents of it are appended to the RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS environment variable which is passed to the RabbitMQ server startup script. Kolla Ansible already configures RabbitMQ server for IPv6 (if necessary). Any argument can be passed there as documented in https://www.rabbitmq.com/runtime.html

The default value for rabbitmq_server_additional_erl_args is +S 2:2 +sbwt none +sbwtdcpu none +sbwtdio none.

By default RabbitMQ starts N schedulers where N is the number of CPU cores, including hyper-threaded cores. This is fine when you assume all CPUs are dedicated to RabbitMQ. Its not a good idea in a typical Kolla Ansible setup. Here we go for two scheduler threads (+S 2:2). More details can be found here: https://www.rabbitmq.com/runtime.html#scheduling and here: https://erlang.org/doc/man/erl.html#emulator-flags

The +sbwt none +sbwtdcpu none +sbwtdio none arguments prevent busy waiting of the scheduler, for more details see: https://www.rabbitmq.com/runtime.html#busy-waiting.

High Availability

RabbitMQ offers two features that, when used together, allow for high availability. These are durable queues and classic queue mirroring. Setting the flag om_enable_rabbitmq_high_availability to true will enable both of these features. There are some queue types which are intentionally not mirrored using the exclusionary pattern ^(?!(amq\\.)|(.*_fanout_)|(reply_)).*.

After enabling this value on a running system, there are some additional steps needed to migrate from transient to durable queues.

  1. Stop all OpenStack services which use RabbitMQ, so that they will not attempt to recreate any queues yet.

    kolla-ansible stop --tags <service-tags>
  2. Generate the new config for all services.

    kolla-ansible genconfig
  3. Reconfigure RabbitMQ.

    kolla-ansible reconfigure --tags rabbitmq
  4. Reset the state on each RabbitMQ, to remove the old transient queues and exchanges.

    kolla-ansible rabbitmq-reset-state
  5. Start the OpenStack services again, at which point they will recreate the appropriate queues as durable.

    kolla-ansible deploy --tags <service-tags>