Provide a summary of the following github project readme file, including the purpose of the project, what problems it may be used to solve, and anything the author mentions that differentiates this project from others:Title: Show HN: Docker rollout – Zero Downtime Deployment for Docker-compose
Site: github.com

docker rollout
Zero Downtime Deployment for Docker Compose

Docker CLI plugin that updates Docker Compose services without downtime.
Simply replace docker compose up -d <service> with docker rollout <service> in your deployment scripts. This command will scale the service to 2 instances, wait for the new container to be ready, and then remove the old container.

Features
Installation
Usage
⚠️ Caveats
Sample deployment script
Why?
License

Features

⏳ Zero downtime deployment for Docker Compose services
🐳 Works with Docker Compose and docker-compose
❤️ Supports Docker healthchecks out of the box

Installation
```bash
Create directory for Docker cli plugins
mkdir -p ~/.docker/cli-plugins
Download docker-rollout script to Docker cli plugins directory
curl https://raw.githubusercontent.com/wowu/docker-rollout/master/docker-rollout -o ~/.docker/cli-plugins/docker-rollout
Make the script executable
chmod +x ~/.docker/cli-plugins/docker-rollout
```
Usage
Run docker rollout <name> instead of docker compose up -d <name> to update a service without downtime.
bash
$ docker rollout -f docker-compose.yml <service-name>
Options:

-f | --file FILE - (not required) - Path to compose file, can be specified multiple times, as in docker-compose.
-t | --timeout SECONDS - (not required) - Timeout in seconds to wait for new container to become healthy, if the container has healthcheck defined in Dockerfile or docker-compose.yml. Default: 60
-w | --wait SECONDS - (not required) - Time to wait for new container to be ready if healthcheck is not defined. Default: 10

See examples in examples directory for sample docker-compose.yml files.
⚠️ Caveats

Currently only services with scale 1 are supported.
Your service cannot have container_name and ports defined in docker-compose.yml, as it's not possible to run multiple containers with the same name or port mapping. Use a proxy as described below.
Proxy like Traefik or nginx-proxy is required to route traffic.
Each deployment will increment the index in container name (e.g. project-web-1 -> project-web-2).

Sample deployment script
Sample deployment script for web service:
```bash
Download latest code
git pull
Build new app image
docker compose build web
Run database migrations
docker compose run web rake db:migrate
Deploy new version
docker rollout web
```
Why?
Using docker compose up to deploy a new version of a service causes downtime because the app container is stopped before the new container is created.
If your application takes a while to boot, this may be noticeable to users.
Using container orchestration tools like Kubernetes or Nomad is usually an overkill for projects that will do fine with a single-server Docker Compose setup. Dokku comes with zero-downtime deployment and more useful features, but it's not as flexible as Docker Compose.
If you have a proxy like Traefik or nginx-proxy, a zero downtime deployment can be achieved by writing a script that scales the service to 2 instances, waits for the new container to be ready, and then removes the old container.
docker rollout does exactly that, but with a single command that you can use in your deployment scripts.
If you're using Docker healthchecks, Traefik will make sure that traffic is only routed to the new container when it's ready.
License
MIT License © Karol Musur