Simple, zero-downtime deploys with nginx and docker-compose

zero_downtime_deploy.sh

#!/bin/bash

# Simple, zero-downtime deploys with nginx and docker-compose
# Thanks to Stephen O'Brien, Head of Product, Tines
# Source: https://www.tines.com/blog/simple-zero-downtime-deploys-with-nginx-and-docker-compose

set -e
set -x

compose_yml="${1:-docker-compose.yml}"

reload_nginx() {  
  docker compose exec nginx /usr/sbin/nginx -s reload || sudo /usr/sbin/nginx -s reload
}

zero_downtime_deploy() {  
  service_name=web
  old_container_id=$(docker ps -f name=$service_name -q | tail -n1)

  # bring a new container online, running new code  
  # (nginx continues routing to the old container only)  
  docker compose -f "$compose_yml" build --pull $service_name
  docker compose -f "$compose_yml" up -d --no-deps --scale $service_name=2 --no-recreate $service_name

  # wait for new container to be available  
  new_container_id=$(docker ps -f name=$service_name -q | head -n1)
  new_container_ip=$(docker inspect -f '{{range.NetworkSettings.Networks}}{{.IPAddress}}{{end}}' "$new_container_id")
  docker compose -f "$compose_yml" exec web \
    curl --silent --include --retry-connrefused \
      --retry 30 --retry-delay 1 --fail --connect-timeout 2 --location \
      http://$new_container_ip:8000/ > /dev/null || exit 1

  # start routing requests to the new container (as well as the old)  
  reload_nginx

  # take the old container offline  
  docker stop "$old_container_id"
  docker rm "$old_container_id"

  docker compose -f "$compose_yml" up -d --no-deps --scale $service_name=1 --no-recreate $service_name

  # stop routing requests to the old container  
  reload_nginx
}

zero_downtime_deploy