Update Zulip Server version

Context: This procedure was written at the time of Zulip 11.4, and applies to upgrades performed on the chat.dsinternal.net server.

Important Notes

• It is possible (and supported) to upgrade across multiple versions at once — there is no need to install each intermediate release.
• Always consult the official Zulip upgrade documentation first. It supersedes this checklist:

https://zulip.readthedocs.io/en/latest/production/upgrade.html

• Make sure to note any important and relevant details concerning the next upgrade(s) reading the upgrade notes for every upcoming major version:

https://zulip.readthedocs.io/en/latest/overview/changelog.html

• In our case we're following the upgrading-to-a-release method not the upgrading-from-a-git-repository one.
• Read any version-specific upgrade notes in the official docs before proceeding.

Pre-upgrade Steps

1. Read the https://zulip.readthedocs.io/en/latest/overview/changelog.html and prepare accordingly if some specific actions need to be taken
2. Make sure the Debian and PostgreSQL versions are compatible with the upcoming update
3. Schedule and announce the maintenance window
4. Create a maintenance period in Zabbix
5. Create a backup and/or snapshot

Upgrade Procedure

Important Notes This procedure is taken from the official doc, if official doc has been updated this checklist should be updated to

1. Fetch the latest build curl -fLO https://download.zulip.com/server/zulip-server-latest.tar.gz
2. Run the upgrade /home/zulip/deployments/current/scripts/upgrade-zulip zulip-server-latest.tar.gz
3. Monitor the process, expect temporary CPU and memory spikes right after the upgrade due to migrations and cache rebuilds. You probably want to wait for things to settle down before going on to next steps.

Post-upgrade Tasks

1. Update the settings.py file following the method described here
2. Once you've made sure everything is running as expected remove the snapshot and maintenance period