How to fix ERROR 2005 (HY000): Unknown MySQL server host in MySQL

# Correct format examples:
mysql -h localhost -u root -p
mysql -h 127.0.0.1 -u root -p
mysql -h db.example.com -u root -p
mysql -h mysql-server -u root -p  # Docker container name

# INCORRECT formats that cause Error 2005:
mysql -h http://localhost -u root -p          # ❌ Do not include http://
mysql -h localhost:3306 -u root -p            # ❌ Port in hostname
mysql -h "localhost 3306" -u root -p         # ❌ Space instead of colon
mysql -h local host -u root -p               # ❌ Space in hostname
mysql -h localhost. -u root -p                # ❌ Trailing dot

# Correct: separate -h and -P options
mysql -h db.example.com -P 3306 -u root -p

# Correct: default port (3306) does not need -P
mysql -h db.example.com -u root -p

# If using non-default port:
mysql -h 192.168.1.10 -P 3307 -u root -p

# For TCP socket connections (Windows):
mysql -h . -u root -p  # Dot means localhost via TCP

# Linux/Mac: Use nslookup or dig
nslookup db.example.com
dig db.example.com
host db.example.com

# Windows: Use nslookup
nslookup db.example.com

# All platforms: Use ping to test both resolution and reachability
ping db.example.com

# If nslookup returns "server can't find db.example.com":
# - Hostname does not exist in DNS
# - DNS server is wrong
# - Network has no DNS connectivity

# Linux/Mac: Edit /etc/hosts
127.0.0.1 db.local

# Windows: Edit C:\Windows\System32\drivers\etc\hosts
127.0.0.1 db.local

# Then connect:
mysql -h db.local -u root -p

# Ping the resolved IP:
ping 203.0.113.45

# Check if MySQL port (3306) is reachable:
telnet 203.0.113.45 3306
# or using netcat:
nc -zv 203.0.113.45 3306

# On Mac/Linux, use bash timeout to avoid hanging:
timeout 5 bash -c "cat < /dev/null > /dev/tcp/203.0.113.45/3306" && echo "Port open" || echo "Port closed"

# Docker Compose: use service name from docker-compose.yml
mysql -h mysql -u root -p  # "mysql" is the service name

# Docker (bridged network): use container name or IP
mysql -h mysql-container -u root -p

# Kubernetes: use the service DNS name
mysql -h mysql-service.default.svc.cluster.local -u root -p

# Find your service IP:
kubectl get svc

# AWS RDS endpoint example:
mysql -h my-database.c9akciq32.us-east-1.rds.amazonaws.com -u admin -p

# Azure endpoint example:
mysql -h myserver.mysql.database.azure.com -u admin@myserver -p

# Verify the endpoint in your cloud console:
# AWS: RDS Dashboard > Databases > Endpoint
# Azure: MySQL Server > Overview > Server name
# Google Cloud: Cloud SQL Instances > Connection name

# Ensure your client IP is in the security group (AWS) or firewall rules (Azure):
# AWS: RDS > Security group > Inbound rules > MYSQL/Aurora 3306
# Azure: Connection security > Add current client IP

// Node.js / mysql2 - CORRECT
const connection = mysql.createConnection({
  host: 'db.example.com',
  user: 'root',
  password: 'secret',
  database: 'mydb'
});

// INCORRECT - includes port in host
const connection = mysql.createConnection({
  host: 'db.example.com:3306',  // ❌ Error 2005
  user: 'root'
});

// INCORRECT - includes protocol
const connection = mysql.createConnection({
  host: 'https://db.example.com',  // ❌ Error 2005
  user: 'root'
});

// CORRECT - port separate
const connection = mysql.createConnection({
  host: 'db.example.com',
  port: 3306,
  user: 'root',
  password: 'secret',
  database: 'mydb'
});