How to fix ERR Failed to resolve hostname in Redis

First, confirm that the hostname you're trying to connect to is correct and can be resolved. Test DNS resolution using standard tools:

# Using nslookup
nslookup redis-server.example.com

# Using dig for more detailed information
dig redis-server.example.com

# Using ping to test connectivity
ping redis-server.example.com

If these commands fail to resolve the hostname, the issue is a DNS problem, not Redis. Check that the hostname exists and is registered in DNS.

If hostname resolution failed, try connecting using the IP address instead. First, get the IP address:

nslookup redis-server.example.com
# Look for the "Address:" field in the output

Then test Redis connection with the IP:

redis-cli -h 192.0.2.1 -p 6379 ping

If this works, the Redis server is fine—the problem is DNS resolution. If this also fails, the server itself may be unreachable.

Verify that your system's DNS configuration is correct:

# Check DNS servers
cat /etc/resolv.conf

Look for nameserver entries. Common valid configurations include:
- nameserver 8.8.8.8 (Google DNS)
- nameserver 1.1.1.1 (Cloudflare DNS)
- Internal DNS servers in your network

If the file is empty or missing, add valid nameservers:

# Edit the file (requires sudo)
sudo nano /etc/resolv.conf

# Add nameservers if missing
nameserver 8.8.8.8
nameserver 8.8.4.4

If running Redis in Docker, ensure proper networking:

Using docker-compose:

version: '3'
services:
  redis:
    image: redis:latest
    networks:
      - backend

  app:
    image: myapp:latest
    networks:
      - backend
    environment:
      REDIS_HOST: redis  # Use service name, not localhost

networks:
  backend:

Verify containers are on the same network:

docker network ls
docker network inspect <network-name>

Connect using the service name (e.g., redis), not localhost or 127.0.0.1.

In Kubernetes, ensure DNS resolution is working within the cluster:

Check if CoreDNS is running:

kubectl get pods -n kube-system | grep coredns

Test DNS resolution from a pod:

kubectl run -it --rm debug --image=busybox -- sh
# Inside the pod, test:
nslookup redis-service.default.svc.cluster.local

For Redis Sentinel in Kubernetes, use fully qualified domain names:

redis-master-0.redis.default.svc.cluster.local
redis-master-1.redis.default.svc.cluster.local

If using Redis Sentinel 6.2 or later, explicitly enable hostname resolution in your sentinel.conf:

# Edit sentinel.conf
sudo nano /etc/redis/sentinel.conf

# Add these lines:
sentinel resolve-hostnames yes
sentinel announce-hostnames yes

Then restart Sentinel:

sudo systemctl restart redis-sentinel

For earlier Redis versions (< 6.2), you must use IP addresses instead of hostnames in configuration.

Ensure that DNS queries (port 53) and Redis connections (port 6379) are not blocked:

# Test DNS port
nc -zv 8.8.8.8 53

# Test Redis port
nc -zv redis-server.example.com 6379

# Check firewall rules (on Linux with ufw)
sudo ufw status

If blocked, add firewall rules:

# Allow outbound DNS
sudo ufw allow out 53/udp

# Allow Redis connections
sudo ufw allow 6379/tcp