Getting started

Default configuration

At the initial deployment, the role will disable the default Redis Sentinel instance configuration defined by the distribution packages. Next, a new, systemd-based instance will be created with the configuration like TCP ports and UNIX socket the same as the default Redis Sentinel setup. This should allow easy creation of additional Redis Sentinel instances when necessary.

Keep in mind that once the sentine.conf configuration file is generated, the role will not modify it. You should design the required Redis Sentinel setup in a development environment, and then deploy it in production. To reconfigure an instance from scratch, you can remove it by setting its state to absent, and then re-create it again.

Access control and autorization

The debops.redis_server role configures Redis Server instances with a randomly generated password, the same for all instances in the same domain. The password is stored in the secret/ directory on the Ansible Controller (see debops.secret role for details).

The debops.redis_sentinel role will use the same password retrieved from the secret/ directory for the monitor configuration.

Redis password is also exposed in the Ansible local facts, so that other Ansible roles can use it to configure access to Redis by other applications. Run the /etc/ansible/facts.d/redis_sentinel.fact script on the remote host to see the local fact structure and contents.

Example inventory

To enable Redis Sentinel configuration on a host, it needs to be added to a specific Ansible inventory group:

[debops_service_redis_sentinel]
hostname

By default Redis listens only for local connections on the loopback network interface. If you want to set up a cluster of Redis instances on different hosts that talk to each other, you should configure the default instance to bind to all network interfaces, as well as open the TCP ports in the firewall:

# Listen to TCP connections on all interfaces
redis_sentinel__bind: [ '0.0.0.0', '::' ]

# Allow connections to Redis from specific subnets
redis_sentinel__allow: [ '192.0.2.0/24', '2001:db8::/32' ]

You should also tell the default monitor to use the public IP address of a host instead of localhost, this address is shared between Sentinel instances - you should ensure that each instance sees has the same "view" of the Redis cluster:

redis_sentinel__monitors:
  - name: 'redis-ha'
    host: '{{ ansible_fqdn }}'

Example playbook

If you are using this role without DebOps, here's an example Ansible playbook that uses the debops.redis_sentinel role:

---

- name: Manage Redis Sentinel service
  hosts: [ 'debops_service_redis_sentinel' ]
  become: True

  environment: '{{ inventory__environment | d({})
                   | combine(inventory__group_environment | d({}))
                   | combine(inventory__host_environment  | d({})) }}'

  roles:

    - role: debops.redis_sentinel/env
      tags: [ 'role::redis_sentinel', 'role::ferm' ]

    - role: debops.apt_preferences
      tags: [ 'role::apt_preferences', 'skip::apt_preferences' ]
      apt_preferences__dependent_list:
        - '{{ redis_sentinel__apt_preferences__dependent_list }}'

    - role: debops.etc_services
      tags: [ 'role::etc_services', 'skip::etc_services' ]
      etc_services__dependent_list:
        - '{{ redis_sentinel__etc_services__dependent_list }}'

    - role: debops.ferm
      tags: [ 'role::ferm', 'skip::ferm' ]
      ferm__dependent_rules:
        - '{{ redis_sentinel__ferm__dependent_rules }}'

    - role: debops.python
      tags: [ 'role::python', 'skip::python', 'role::redis_sentinel' ]
      python__dependent_packages3:
        - '{{ redis_sentinel__python__dependent_packages3 }}'
      python__dependent_packages2:
        - '{{ redis_sentinel__python__dependent_packages2 }}'

    - role: debops.redis_sentinel
      tags: [ 'role::redis_sentinel', 'skip::redis_sentinel' ]

Ansible tags

You can use Ansible --tags or --skip-tags parameters to limit what tasks are performed during Ansible run. This can be used after a host was first configured to speed up playbook execution, when you are sure that most of the configuration is already in the desired state.

Available role tags:

role::redis_sentinel
Main role tag, should be used in the playbook to execute all of the role tasks as well as role dependencies.

Other resources

List of other useful resources related to the debops.redis_sentinel Ansible role: