--- stage: Enablement group: Distribution info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments type: reference --- # How to set up Consul **(PREMIUM SELF)** A Consul cluster consists of both [server and client agents](https://www.consul.io/docs/agent). The servers run on their own nodes and the clients run on other nodes that in turn communicate with the servers. GitLab Premium includes a bundled version of [Consul](https://www.consul.io/) a service networking solution that you can manage by using `/etc/gitlab/gitlab.rb`. ## Prerequisites Before configuring Consul: 1. Review the [reference architecture](reference_architectures/index.md#available-reference-architectures) documentation to determine the number of Consul server nodes you should have. 1. If necessary, ensure the [appropriate ports are open](package_information/defaults.md#ports) in your firewall. ## Configure the Consul nodes On _each_ Consul server node: 1. Follow the instructions to [install](https://about.gitlab.com/install/) GitLab by choosing your preferred platform, but do not supply the `EXTERNAL_URL` value when asked. 1. Edit `/etc/gitlab/gitlab.rb`, and add the following by replacing the values noted in the `retry_join` section. In the example below, there are three nodes, two denoted with their IP, and one with its FQDN, you can use either notation: ```ruby # Disable all components except Consul roles ['consul_role'] # Consul nodes: can be FQDN or IP, separated by a whitespace consul['configuration'] = { server: true, retry_join: %w(10.10.10.1 consul1.gitlab.example.com 10.10.10.2) } # Disable auto migrations gitlab_rails['auto_migrate'] = false ``` 1. [Reconfigure GitLab](restart_gitlab.md#omnibus-gitlab-reconfigure) for the changes to take effect. 1. Run the following command to ensure Consul is both configured correctly and to verify that all server nodes are communicating: ```shell sudo /opt/gitlab/embedded/bin/consul members ``` The output should be similar to: ```plaintext Node Address Status Type Build Protocol DC CONSUL_NODE_ONE XXX.XXX.XXX.YYY:8301 alive server 0.9.2 2 gitlab_consul CONSUL_NODE_TWO XXX.XXX.XXX.YYY:8301 alive server 0.9.2 2 gitlab_consul CONSUL_NODE_THREE XXX.XXX.XXX.YYY:8301 alive server 0.9.2 2 gitlab_consul ``` If the results display any nodes with a status that isn't `alive`, or if any of the three nodes are missing, see the [Troubleshooting section](#troubleshooting-consul). ## Upgrade the Consul nodes To upgrade your Consul nodes, upgrade the GitLab package. Nodes should be: - Members of a healthy cluster prior to upgrading the Omnibus GitLab package. - Upgraded one node at a time. Identify any existing health issues in the cluster by running the following command within each node. The command will return an empty array if the cluster is healthy: ```shell curl "http://127.0.0.1:8500/v1/health/state/critical" ``` If the Consul version has changed, you'll see a notice at the end of `gitlab-ctl reconfigure` informing you that Consul needs to be restarted for the new version to be used. Restart Consul one node at a time: ```shell sudo gitlab-ctl restart consul ``` Consul nodes communicate using the raft protocol. If the current leader goes offline, there needs to be a leader election. A leader node must exist to facilitate synchronization across the cluster. If too many nodes go offline at the same time, the cluster loses quorum and doesn't elect a leader due to [broken consensus](https://www.consul.io/docs/architecture/consensus). Consult the [troubleshooting section](#troubleshooting-consul) if the cluster is not able to recover after the upgrade. The [outage recovery](#outage-recovery) may be of particular interest. GitLab uses Consul to store only easily regenerated, transient data. If the bundled Consul wasn't used by any process other than GitLab itself, you can [rebuild the cluster from scratch](#recreate-from-scratch). ## Troubleshooting Consul Below are some useful operations should you need to debug any issues. You can see any error logs by running: ```shell sudo gitlab-ctl tail consul ``` ### Check the cluster membership To determine which nodes are part of the cluster, run the following on any member in the cluster: ```shell sudo /opt/gitlab/embedded/bin/consul members ``` The output should be similar to: ```plaintext Node Address Status Type Build Protocol DC consul-b XX.XX.X.Y:8301 alive server 0.9.0 2 gitlab_consul consul-c XX.XX.X.Y:8301 alive server 0.9.0 2 gitlab_consul consul-c XX.XX.X.Y:8301 alive server 0.9.0 2 gitlab_consul db-a XX.XX.X.Y:8301 alive client 0.9.0 2 gitlab_consul db-b XX.XX.X.Y:8301 alive client 0.9.0 2 gitlab_consul ``` Ideally all nodes have a `Status` of `alive`. ### Restart Consul If it is necessary to restart Consul, it is important to do this in a controlled manner to maintain quorum. If quorum is lost, to recover the cluster, you follow the Consul [outage recovery](#outage-recovery) process. To be safe, it's recommended that you only restart Consul in one node at a time to ensure the cluster remains intact. For larger clusters, it is possible to restart multiple nodes at a time. See the [Consul consensus document](https://www.consul.io/docs/architecture/consensus#deployment-table) for the number of failures it can tolerate. This will be the number of simultaneous restarts it can sustain. To restart Consul: ```shell sudo gitlab-ctl restart consul ``` ### Consul nodes unable to communicate By default, Consul attempts to [bind](https://www.consul.io/docs/agent/options#_bind) to `0.0.0.0`, but it advertises the first private IP address on the node for other Consul nodes to communicate with it. If the other nodes cannot communicate with a node on this address, then the cluster has a failed status. If you run into this issue, then messages like the following are output in `gitlab-ctl tail consul`: ```plaintext 2017-09-25_19:53:39.90821 2017/09/25 19:53:39 [WARN] raft: no known peers, aborting election 2017-09-25_19:53:41.74356 2017/09/25 19:53:41 [ERR] agent: failed to sync remote state: No cluster leader ``` To fix this: 1. Pick an address on each node that all of the other nodes can reach this node through. 1. Update your `/etc/gitlab/gitlab.rb` ```ruby consul['configuration'] = { ... bind_addr: 'IP ADDRESS' } ``` 1. Reconfigure GitLab; ```shell gitlab-ctl reconfigure ``` If you still see the errors, you may have to [erase the Consul database and reinitialize](#recreate-from-scratch) on the affected node. ### Consul does not start - multiple private IPs If a node has multiple private IPs, Consul doesn't know about which of the private addresses to advertise, and then it immediately exits on start. Messages like the following are output in `gitlab-ctl tail consul`: ```plaintext 2017-11-09_17:41:45.52876 ==> Starting Consul agent... 2017-11-09_17:41:45.53057 ==> Error creating agent: Failed to get advertise address: Multiple private IPs found. Please configure one. ``` To fix this: 1. Pick an address on the node that all of the other nodes can reach this node through. 1. Update your `/etc/gitlab/gitlab.rb` ```ruby consul['configuration'] = { ... bind_addr: 'IP ADDRESS' } ``` 1. Reconfigure GitLab; ```shell gitlab-ctl reconfigure ``` ### Outage recovery If you have lost enough Consul nodes in the cluster to break quorum, then the cluster is considered to have failed and cannot function without manual intervention. In that case, you can either recreate the nodes from scratch or attempt a recover. #### Recreate from scratch By default, GitLab does not store anything in the Consul node that cannot be recreated. To erase the Consul database and reinitialize: ```shell sudo gitlab-ctl stop consul sudo rm -rf /var/opt/gitlab/consul/data sudo gitlab-ctl start consul ``` After this, the node should start back up, and the rest of the server agents rejoin. Shortly after that, the client agents should rejoin as well. #### Recover a failed node If you have taken advantage of Consul to store other data and want to restore the failed node, follow the [Consul guide](https://learn.hashicorp.com/tutorials/consul/recovery-outage) to recover a failed cluster.