Blue-green deployment

The strategy consists of keeping two simultaneous instances of the same app. Both of equal importance, hence the use of colors for naming. The trick is in being able to change routes and dns from one to the other instantly as to allow mechanized deployment and rollbacks.

While reading on the subject I found an example made by someone on Medium by using some bash scripting and nginx. It seems this is done by changing the site’s nginx conf file with sed, changing proxy_pass from blue port to green port or viceversa.

#!/bin/bash
 
# Configuration
BLUE_DIR="/path/to/nextjs-blue"
GREEN_DIR="/path/to/nextjs-green"
GREEN_PORT="3001" # Port on which Green runs
BLUE_PORT="3000" # Port on which Blue runs
NGINX_CONFIG="/etc/nginx/sites-available/nextjs"
GITHUB_REPO="https://github.com/your-username/your-repo.git"
 
# Determine which environment is currently running (Blue or Green)
CURRENT_PORT=$(grep -oP 'proxy_pass http://localhost:\K\d+' $NGINX_CONFIG)
# Determine the old PM2 process name
OLD_NAME=""
TARGET_DIR=""
 
if [ "$CURRENT_PORT" == "$BLUE_PORT" ]; then
    TARGET_DIR=$GREEN_DIR
    TARGET_PORT=$GREEN_PORT
    OLD_NAME=$(basename $GREEN_DIR)
else
    TARGET_DIR=$BLUE_DIR
    TARGET_PORT=$BLUE_PORT
    OLD_NAME=$(basename $BLUE_DIR)
fi
 
# Step 1: Pull from GitHub into target environment
echo "Pulling latest code into target environment ($TARGET_DIR)..."
cd $TARGET_DIR
git pull $GITHUB_REPO
 
# Step 2: Yarn Build for target version
echo "Building target environment..."
yarn install
yarn build
 
# Start/Restart the target environment using PM2
TARGET_NAME=$(basename $TARGET_DIR)
pm2 stop $TARGET_NAME
pm2 delete $TARGET_NAME
pm2 start yarn --name "$TARGET_NAME" -- start -p $TARGET_PORT || pm2 restart $TARGET_NAME
 
echo "Stopping old environment ($OLD_NAME)..."
pm2 stop $OLD_NAME
pm2 delete $OLD_NAME
 
pm2 save
 
# Allow a few seconds for the server to start
sleep 5
 
# Step 3: Check if target version index page returns 200
echo "Checking target environment health..."
STATUS_CODE=$(curl -o /dev/null -s -w "%{http_code}" http://localhost:$TARGET_PORT)
 
if [ "$STATUS_CODE" -ne 200 ]; then
    echo "Target environment health check failed with status code: $STATUS_CODE"
    exit 1
fi
 
# Step 4: Switch Nginx to target environment
echo "Switching Nginx to target environment..."
sed -i "s/proxy_pass http:\/\/localhost:[0-9]*;/proxy_pass http:\/\/localhost:$TARGET_PORT;/" $NGINX_CONFIG
nginx -s reload
 
echo "Deployment complete. Target environment ($TARGET_NAME) is now live!"

— medium post

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Sources

https://medium.com/@feyzilim/blue-green-deployments-for-next-js-using-pm2-nginx-and-github-22cae8893af7 https://en.wikipedia.org/wiki/Blue%E2%80%93green_deployment https://martinfowler.com/bliki/BlueGreenDeployment.html