Currently, I have set the target group to port 80 through EC2 load balancing. The status shows as "Unhealthy", and the health check details indicate "Health checks failed with these codes: \[502\]". The health check is set to /actuator/health (with dependency injection in gradle and configuration in application.properties).

This error occurred while implementing Docker, Nginx, and Blue-Green deployment. The server also shows CORS errors. Nginx is configured to pull the image from Docker.

In the instance, I have configured docker-compose.blue.yml, docker-compose.nginx.yml, docker-compose.green.yml, api.conf, upstream.conf, nginx.conf, current_env.txt, deploy.sh, health_check.sh, and switch.sh.

Here are the configurations in order:

docker-compose.blue.yml

version: '3.8'

services:
  api:
    image: ${DOCKER_REGISTRY}/[docker-repository]:${IMAGE_TAG}
    container_name: api-blue
    restart: unless-stopped
    environment:
      - SERVER_PORT=8080
    ports:
      - "8001:8080"
    networks:
      - app-network
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "3"

networks:
  app-network:
    external: true

docker-compose.nginx.yml

version: '3.8'

services:
  nginx:
    image: nginx:1.21-alpine
    container_name: nginx-proxy
    restart: always
    ports:
      - "80:80"
    volumes:
      - ~/app/nginx/nginx.conf:/etc/nginx/nginx.conf:ro
      - ~/app/nginx/conf.d:/etc/nginx/conf.d:ro
      - /var/log/nginx:/var/log/nginx
    networks:
      - app-network

networks:
  app-network:
    external: true

docker-compose.green.yml

version: '3.8'

services:
  api:
    image: ${DOCKER_REGISTRY}/[docker-repository]:${IMAGE_TAG} 
    container_name: api-green
    restart: unless-stopped
    environment:
      - SERVER_PORT=8080
    ports:
      - "8002:8080"  
    networks:
      - app-network
    logging:
      driver: "json-file"
      options:
        max-size: "10m"
        max-file: "3"

networks:
  app-network:
    external: true

api.conf

server {
    listen 80;
    server_name [backend-server]; 
    
    access_log /var/log/nginx/api-access.log;
    error_log /var/log/nginx/api-error.log;

    location /actuator/health { 
        add_header 'Access-Control-Allow-Origin' '[frontend-server]' always; 
        add_header 'Access-Control-Allow-Credentials' 'true' always;
        proxy_pass http://app_server/api/health;

        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded_For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded_Proto $scheme;
        
        proxy_connect_timeout 5s;
        proxy_send_timeout 5s;
        proxy_read_timeout 5s;
        
        access_log /var/log/nginx/health-access.log;
        error_log /var/log/nginx/health-error.log debug;
    }
    
    location /health/blue {
        proxy_pass http://blue/api/health;
        access_log off;
    }
    
    location /health/green {
        proxy_pass http://green/api/health;
        access_log off;
    }
    
    location / {
        
        add_header 'Access-Control-Allow-Origin' '' always;
        add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS, PUT, DELETE' always;
        add_header 'Access-Control-Allow-Headers' 'DNT,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Range,Authorization' always;
        add_header 'Access-Control-Allow-Credentials' 'true' always;
        
        
        if ( $request_method = 'OPTIONS') {
            add_header 'Access-Control-Max-Age' 1728000;
            add_header 'Content-Type' 'text/plain charset=UTF-8';
            add_header 'Content-Length' 0;
            return 204;
        }
        
        proxy_pass http://app_server;
        proxy_http_version 1.1;
        proxy_set_header Host $host;  
        proxy_set_header X-Real-IP $remote_addr;  
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;  
        proxy_connect_timeout 60s;
        proxy_send_timeout 60s;
        proxy_read_timeout 60s;
    }
}

upstream.conf

upstream blue {
    server 127.0.0.1:8001;
}

upstream green {
    server 127.0.0.1:8002;
}

upstream app_server {
    server 127.0.0.1:8002;
}

nginx.conf

user  nginx;
worker_processes  auto;

error_log  /var/log/nginx/error.log notice;
pid        /var/run/nginx.pid;

events {
    worker_connections  1024;
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    keepalive_timeout  65;

    include /etc/nginx/conf.d/*.conf;
}

current_env.txt -> blue or green

deploy.sh

#!/bin/bash
source ~/app/.env

DOCKER_USERNAME=${DOCKER_USERNAME:-"tmakxmgkdntn"}
IMAGE_TAG=$1
APP_NAME=${2:-"[docker-repository]"}

ENV_FILE=~/app/scripts/current_env.txt
if [ ! -f "$ENV_FILE" ]; then
    echo "blue" > "$ENV_FILE"
fi

BLUE_RUNNING=$(docker ps | grep api-blue | wc -l)
GREEN_RUNNING=$(docker ps | grep api-green | wc -l)

if [ "$BLUE_RUNNING" -eq 1 ] && [ "$GREEN_RUNNING" -eq 0 ]; then
    echo "blue" > "$ENV_FILE"
elif [ "$BLUE_RUNNING" -eq 0 ] && [ "$GREEN_RUNNING" -eq 1 ]; then
    echo "green" > "$ENV_FILE"
elif [ "$BLUE_RUNNING" -eq 0 ] && [ "$GREEN_RUNNING" -eq 0 ]; then
    echo "blue" > "$ENV_FILE"
fi

CURRENT_ENV=$(cat "$ENV_FILE")
DEPLOY_ENV=$([ "$CURRENT_ENV" == "blue" ] && echo "green" || echo "blue")

echo "Current environment: $CURRENT_ENV"
echo "Deploying to: $DEPLOY_ENV"
echo "Using image: $DOCKER_USERNAME/$APP_NAME:$IMAGE_TAG"

echo "Pulling Docker image: $DOCKER_USERNAME/$APP_NAME:$IMAGE_TAG"
if docker pull $DOCKER_USERNAME/$APP_NAME:$IMAGE_TAG; then
  docker images | grep $IMAGE_TAG
else
  exit 1
fi

export DOCKER_REGISTRY=$DOCKER_USERNAME
export IMAGE_TAG=$IMAGE_TAG

echo "Starting service in $DEPLOY_ENV environment..."
cd ~/app/$DEPLOY_ENV
docker-compose -f docker-compose.$DEPLOY_ENV.yml down --remove-orphans
docker-compose -f docker-compose.$DEPLOY_ENV.yml up -d

if [ $? -ne 0 ]; then
    exit 1
fi

echo "Waiting for service to be healthy..."
~/app/scripts/health_check.sh $DEPLOY_ENV

if [ $? -ne 0 ]; then
    echo "Health check failed. Rolling back..."
    docker-compose -f docker-compose.$DEPLOY_ENV.yml down
    exit 1
fi

echo "Switching traffic to $DEPLOY_ENV environment..."
~/app/scripts/switch.sh $DEPLOY_ENV

if [ $? -ne 0 ]; then
    echo "Traffic switch failed. Rolling back..."
    exit 1
fi

echo $DEPLOY_ENV > ~/app/scripts/current_env.txt

9. health_check.sh
#!/bin/bash
ENV=$1
MAX_RETRIES=30
RETRY_INTERVAL=2
PORT=$([ "$ENV" == "blue" ] && echo "8001" || echo "8002")
ENDPOINT="http://localhost:$PORT/actuator/health"

for i in $(seq 1 $MAX_RETRIES); do
    RESPONSE=$(curl -s -w "%{http_code}" $ENDPOINT)
    HTTP_CODE=$(echo "$RESPONSE" | tail -c 4)
    HTTP_BODY=$(echo "$RESPONSE" | head -c -4)

    if [ "$HTTP_CODE" == "200" ]; then
        if echo "$HTTP_BODY" | grep -qE '"status":"UP"|"UP"'; then
            exit 0
        fi
    fi

    sleep $RETRY_INTERVAL
done

exit 1

health_check.sh

#!/bin/bash
ENV=$1
MAX_RETRIES=30
RETRY_INTERVAL=2
PORT=$([ "$ENV" == "blue" ] && echo "8001" || echo "8002")
ENDPOINT="http://localhost:$PORT/actuator/health"

for i in $(seq 1 $MAX_RETRIES); do
    RESPONSE=$(curl -s -w "%{http_code}" $ENDPOINT)
    HTTP_CODE=$(echo "$RESPONSE" | tail -c 4)
    HTTP_BODY=$(echo "$RESPONSE" | head -c -4)

    if [ "$HTTP_CODE" == "200" ]; then
        if echo "$HTTP_BODY" | grep -qE '"status":"UP"|"UP"'; then
            exit 0
        fi
    fi

    sleep $RETRY_INTERVAL
done

exit 1

switch.sh

#!/bin/bash
NEW_ENV=$1
NGINX_CONF_PATH=~/app/nginx/conf.d/upstream.conf

echo "Switching traffic to $NEW_ENV environment..."

sed -i "s/server 127.0.0.1:.*/server 127.0.0.1:$([ "$NEW_ENV" == "blue" ] && echo "8001" || echo "8002");/" "$NGINX_CONF_PATH"

docker exec nginx-proxy nginx -t

if [ $? -eq 0 ]; then
    echo "Nginx configuration test passed. Reloading Nginx..."
    docker exec nginx-proxy nginx -s reload
    echo "Traffic switched to $NEW_ENV environment."
else
    echo "Nginx configuration test failed. Rolling back..."
    exit 1
fi

When I check directly inside the Docker container using curl, everything works fine. However, since the status is still unhealthy, I believe there is an issue with my Nginx configuration. Could you help me identify the problem or suggest something I should study to resolve this issue? I’m a beginner, but I’m willing to put in the effort.

If any additional code is needed, please let me know. thanks..