GitLab Geo troubleshooting

Note: This list is an attempt to document all the moving parts that can go wrong. We are working into getting all this steps verified automatically in a rake task in the future.

Setting up Geo requires careful attention to details and sometimes it's easy to miss a step. Here is a checklist of questions you should ask to try to detect where you have to fix (all commands and path locations are for Omnibus installs):

Is Postgres replication working?
Are my nodes pointing to the correct database instance?
- You should make sure your primary Geo node points to the instance with writing permissions.
- Any secondary nodes should point only to read-only instances.
Can Geo detect my current node correctly?
- Geo uses your defined node from Admin ➔ Geo screen, and tries to match with the value defined in /etc/gitlab/gitlab.rb configuration file. The relevant line looks like: external_url "http://gitlab.example.com".
- To check if node on current machine is correctly detected type:
```
sudo gitlab-rails runner "puts Gitlab::Geo.current_node.inspect"
```
  and expect something like:
```
#<GeoNode id: 2, schema: "https", host: "gitlab.example.com", port: 443, relative_url_root: "", primary: false, ...>
```
- By running the command above, primary should be true when executed in the primary node, and false on any secondary
Did I define the correct SSH Key for the node?
- You must create an SSH Key for git user
- This key is the one you have to inform at Admin > Geo
Can I SSH from secondary to primary node using git user account?
- This is the most obvious cause of problems with repository replication issues. If you haven't added the primary node's key to known_hosts, you will end up with a lot of failed sidekiq jobs with an error similar to:
```
Gitlab::Shell::Error: Host key verification failed. fatal: Could not read from remote repository. Please make sure you have the correct access rights and the repository exists.
```
  An easy way to fix is by logging in as the git user in the secondary node and run:
```
# remove old entries to your primary gitlab in known_hosts
ssh-keyscan -R your-primary-gitlab.example.com
```
How do I fix the message, "ERROR: replication slots can only be used if max_replication_slots > 0"?
- This means that the max_replication_slots PostgreSQL variable needs to be set on the primary database. In GitLab 9.4, we have made this setting default to 1. You may need to increase this value if you have more Geo secondary nodes. Be sure to restart PostgreSQL for this to take effect. See the PostgreSQL replication setup guide for more details.
How do I fix the message, "FATAL: could not start WAL streaming: ERROR: replication slot "geo_secondary_my_domain_com" does not exist"?
- This occurs when PostgreSQL does not have a replication slot for the secondary by that name. You may want to rerun the replication process on the secondary.

Visit the primary node's Admin Area ➔ Geo Nodes (/admin/geo_nodes) in your browser. We perform the following health checks on each secondary node to help identify if something is wrong:

Is the node running?
Is the node's secondary database configured for streaming replication?
Is the node's secondary tracking database configured?
Is the node's secondary tracking database connected?
Is the node's secondary tracking database up-to-date?