Consul

Install and configure a Consul agent.

The agent can act as a client or as a server if the host is placed in a group called consul in the inventory.

Variables

• consul_version: The version of Consul to install.
• consul_bind_address: The address that should be bound to for internal cluster communications. This is an IP address that should be reachable by all other nodes in the cluster.
• consul_advertise_address: The advertise address is used to change the address that we advertise to other nodes in the cluster. By default, the -bind address is advertised.
• consul_client_address: The address to which Consul will bind client interfaces, including the HTTP, DNS, and RPC servers. By default, this is "127.0.0.1", allowing only loopback connections.
• consul_datacenter: The datacenter in which the agent is running.
• consul_domain: By default, Consul responds to DNS queries in the "consul." domain. This flag can be used to change that domain. All queries in this domain are assumed to be handled by Consul and will not be recursively resolved.
• consul_retry_join: Addresses of other agents to join upon starting up.
• consul_retry_join_wan: Addresses of other WAN agents to join upon starting up.
• consul_bootstrap_expect: Number of expected servers in the datacenter. When provided, Consul waits until the specified number of servers are available and then bootstraps the cluster.
• consul_ui_enabled: Whether to enable the UI or not, default is false.
• consul_node_meta: This object allows associating arbitrary metadata key/value pairs with the local node, which can then be used for filtering results from certain catalog endpoints.
• consul_inventory_group_name: set to the group name in the inventory file of the consul servers. Default is 'consul'.
• consul_install_dir: Full path to where to install the consul command. Default is /usr/local/bin.
• consul_reconnect_timeout: This controls how long it takes for a failed node to be completely removed from the cluster.
• consul_reconnect_timeout_wan: This is the WAN equivalent of the reconnect_timeout parameter, which controls how long it takes for a failed server to be completely removed from the WAN pool.
• consul_enable_script_checks: This controls whether health checks that execute scripts are enabled on this agent, and defaults to false so operators must opt-in to allowing these.
• consul_s3_source: Path to a S3 object. If specified, the consul archive will be fetched from this S3 source instead of the hashicorp CDN.

Bootstrapping

All the consul agents are using the retry_join option to know how to join the cluster.

For the initial seed, they all have the IP addresses of the others in their config and will try to reach each other until all the servers specified in the consul group are available (specified by the bootstrap_expect option). When all the servers become available, they will do the election and client will be able to join the cluster too.