Kamal 2: Upgrade Guide

There are some significant differences between Kamal 1 and Kamal 2.

• The Traefik proxy has been replaced by kamal-proxy
• Kamal will run all containers in a custom docker network
• There are some backward incompatible configuration changes
• How we pass secrets to containers has changed

If you want to continue using Traefik you can run it as an accessory, see here for more details.

Upgrade steps

Upgrade to Kamal 1.9.x

If you are planning to do in-place upgrades of servers, you should first upgrade to Kamal 1.9, as it has support for downgrading.

If using gem directly, you can run:

gem install kamal --version 1.9.0

Confirm you can deploy your application with Kamal 1.9.

Upgrade to Kamal 2

If using the gem directly, run:

gem install kamal

Make configuration changes

You’ll need to convert your configuration to work with Kamal 2.

You can test whether the new configuration is valid by running:

$ kamal config

If you have multiple destinations, you should test each ones configuration:

$ kamal config -d staging
$ kamal config -d beta

Move from .env to .kamal/secrets

Follow the steps here.

In-place upgrades

Warning: Test this in a non-production environment first, if possible

Upgrading

You can then upgrade with:

$ kamal upgrade [-d <DESTINATION>]

You’ll need to do this separately for each destination.

The kamal upgrade command will:

1. Stop and remove the Traefik proxy
2. Create a kamal docker network, if one doesn’t exist
3. Start a kamal-proxy container in the new network
4. Reboot the current deployed version of the app container in the new network
5. Tell kamal-proxy to send traffic to it
6. Reboot all accessories in the new network

Avoiding downtime

If you are running your application on multiple servers, and want to avoid downtime you can do a rolling upgrade:

$ kamal upgrade --rolling [-d <DESTINATION>]

This will follow the same steps as above, but host by host.

Alternatively you can run the command host by host:

$ kamal upgrade -h 127.0.0.1[,127.0.0.2]

You could additionally use the pre-proxy-reboot and post-proxy-reboot hooks to manually remove your server from upstream load balancers, to ensure no requests are dropped during the upgrade process.

Downgrading

If you want to reverse your changes and go back to Kamal 1.9.

1. Uninstall Kamal 2.0.
2. Confirm you are running Kamal 1.9, by running kamal version
3. Run the kamal downgrade command. It has the same options as kamal upgrade and will reverse the process

The upgrade and downgrade commands can be re-run against servers that have already been upgraded or downgraded.