MRSK ships zero-downtime deploys of Rails apps packed as containers to any host. It uses the dynamic reverse-proxy Traefik to hold requests while the new application container is started and the old one is wound down. It works across multiple hosts at the same time, using SSHKit to execute commands.
Add the gem with bundle add mrsk, then run rake mrsk:init, and then edit the new file in config/deploy.yml to use the proper service name, image reference, servers to deploy on, and so on. It could look something like this:
service: hey
image: 37s/hey
servers:
- xxx.xxx.xxx.xxx
- xxx.xxx.xxx.xxx
env:
DATABASE_URL: mysql2://db1/hey_production/
REDIS_URL: redis://redis1:6379/1
registry:
server: registry.digitalocean.com
username: <%= Rails.application.credentials.registry["username"] %>
password: <%= Rails.application.credentials.registry["password"] %>Then ensure your encrypted credentials have the registry username + password by editing them with rails credentials:edit:
registry:
username: real-user-name
password: real-password
Now you're ready to deploy a multi-arch image (FIXME: currently you need to manually run docker buildx create --use once first):
rake mrsk:deploy
This will:
- Log into the registry both locally and remotely
- Build the image using the standard Dockerfile in the root of the application.
- Push the image to the registry.
- Pull the image from the registry on the servers.
- Ensure Traefik is running and accepting traffic on port 80.
- Stop any containers running a previous versions of the app.
- Start a new container with the version of the app that matches the current git version hash.
- Prune unused images and stopped containers to ensure servers don't fill up.
Voila! All the servers are now serving the app on port 80. If you're just running a single server, you're ready to go. If you're running multiple servers, you need to put a load balancer in front of them.
You can see the state of your servers by running rake mrsk:info. It'll show something like this:
Traefik Host: xxx.xxx.xxx.xxx
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
6195b2a28c81 traefik "/entrypoint.sh --pr…" 30 minutes ago Up 19 minutes 0.0.0.0:80->80/tcp, :::80->80/tcp traefik
Traefik Host: 164.92.105.119
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
de14a335d152 traefik "/entrypoint.sh --pr…" 30 minutes ago Up 19 minutes 0.0.0.0:80->80/tcp, :::80->80/tcp traefik
App Host: 164.90.145.60
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
badb1aa51db3 registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123 "/rails/bin/docker-e…" 13 minutes ago Up 13 minutes 3000/tcp chat-6ef8a6a84c525b123c5245345a8483f86d05a123
App Host: 164.92.105.119
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1d3c91ed1f55 registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123 "/rails/bin/docker-e…" 13 minutes ago Up 13 minutes 3000/tcp chat-6ef8a6a84c525b123c5245345a8483f86d05a123
You can also see just info for app containers with rake mrsk:app:info or just for Traefik with rake mrsk:traefik:info.
If you've discovered a bad deploy, you can quickly rollback by reactivating the old, paused container image. You can see what old containers are available for rollback by running rake mrsk:app:containers. It'll give you a presentation similar to rake mrsk:app:info, but include all the old containers as well. Showing something like this:
App Host: 164.92.105.119
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1d3c91ed1f51 registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123 "/rails/bin/docker-e…" 19 minutes ago Up 19 minutes 3000/tcp chat-6ef8a6a84c525b123c5245345a8483f86d05a123
539f26b28369 registry.digitalocean.com/user/app:e5d9d7c2b898289dfbc5f7f1334140d984eedae4 "/rails/bin/docker-e…" 31 minutes ago Exited (1) 27 minutes ago chat-e5d9d7c2b898289dfbc5f7f1334140d984eedae4
App Host: 164.90.145.60
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
badb1aa51db4 registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123 "/rails/bin/docker-e…" 19 minutes ago Up 19 minutes 3000/tcp chat-6ef8a6a84c525b123c5245345a8483f86d05a123
6f170d1172ae registry.digitalocean.com/user/app:e5d9d7c2b898289dfbc5f7f1334140d984eedae4 "/rails/bin/docker-e…" 31 minutes ago Exited (1) 27 minutes ago chat-e5d9d7c2b898289dfbc5f7f1334140d984eedae4
From the example above, we can see that e5d9d7c2b898289dfbc5f7f1334140d984eedae4 was the last version, so it's available as a rollback target. We can perform this rollback by running rake mrsk:rollback VERSION=e5d9d7c2b898289dfbc5f7f1334140d984eedae4. That'll stop 6ef8a6a84c525b123c5245345a8483f86d05a123 and then start e5d9d7c2b898289dfbc5f7f1334140d984eedae4. Because the old container is still available, this is very quick. Nothing to download from the registry.
Note that by default old containers are pruned after 3 days when you run rake mrsk:deploy.
...
This is alpha software. Lots of stuff is missing. Here are some of the areas we seek to improve:
- Adapterize commands to work with Podman and other container runners
- Possibly switching to a bin/mrsk command rather than raw rake
- Integrate with cloud CI pipelines
MRSK is released under the MIT License.