How to fix ERR Failed to resolve hostname in Redis

RedisINTERMEDIATEHIGHUpdated Dec 29, 2025· 155 views

The "ERR Failed to resolve hostname" error occurs when Redis or a Redis client cannot resolve a hostname to its IP address through DNS. This is typically caused by DNS configuration issues, network connectivity problems, or incorrect hostname configuration.

Quick fix

Fixes ERR Failed to resolve hostname

# 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
  1. Verify the hostname is correct and resolvable
  2. Test connectivity using the IP address
  3. Check DNS configuration on the system
  4. For Docker containers, use service names and correct networks
redis — error
# 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
ERR Failed to resolve hostname

What this error means

When Redis tries to connect to a host specified by name (rather than IP address), it uses DNS to resolve that hostname to an IP address. If DNS lookup fails—whether due to misconfiguration, network issues, or an invalid hostname—Redis will return this error. This commonly occurs in Redis Sentinel deployments, cluster setups, or when connecting through intermediate services. In some cases, particularly with Redis versions below 6.2 in Sentinel mode, hostname resolution may not be enabled by default, requiring explicit configuration to function.

Typical symptoms

  • Redis connection fails with 'Failed to resolve hostname' error message
  • Redis Sentinel cannot connect to master or slave nodes by hostname
  • Docker containers or Kubernetes pods fail to connect to Redis services
  • Connection works with IP address but fails with hostname
  • Redis cluster nodes cannot communicate with each other by hostname
  • Error appears when trying to replicate or failover in Sentinel setup

Common causes

  1. DNS server is unreachable or not responding to hostname resolution queries
  2. The hostname is misspelled or does not exist in DNS
  3. Network connectivity is blocked between the client and DNS servers (port 53)
  4. Redis Sentinel version is below 6.2 with hostname resolution not explicitly enabled
  5. Container or Kubernetes DNS configuration is incorrect or not properly initialized
  6. Firewall rules are blocking DNS queries or connections to the target host
  7. Redis node is configured to announce a hostname that doesn't exist or isn't resolvable
  8. /etc/resolv.conf is missing or misconfigured on the system

How to fix "ERR Failed to resolve hostname"

1Verify the hostname is correct and resolvable

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

bash
# 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.

2Test connectivity using the IP address

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

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

Then test Redis connection with the IP:

bash
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.

3Check DNS configuration on the system

Verify that your system's DNS configuration is correct:

bash
# 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:

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

# Add nameservers if missing
nameserver 8.8.8.8
nameserver 8.8.4.4
4For Docker containers, use service names and correct networks

If running Redis in Docker, ensure proper networking:

Using docker-compose:

yaml
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:

bash
docker network ls
docker network inspect <network-name>

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

5For Kubernetes, check DNS and service resolution

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

Check if CoreDNS is running:

bash
kubectl get pods -n kube-system | grep coredns

Test DNS resolution from a pod:

bash
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:

bash
redis-master-0.redis.default.svc.cluster.local
redis-master-1.redis.default.svc.cluster.local
6Enable hostname resolution in Redis Sentinel (6.2+)

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

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

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

Then restart Sentinel:

bash
sudo systemctl restart redis-sentinel

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

7Check firewall and network connectivity

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

bash
# 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:

bash
# Allow outbound DNS
sudo ufw allow out 53/udp

# Allow Redis connections
sudo ufw allow 6379/tcp

Advanced notes

Redis Sentinel has specific hostname resolution behavior. In versions prior to 6.2, Sentinel always stored and announced master/slave connection information as IP addresses, making failover problematic in environments with dynamic IPs (like Kubernetes). Redis 6.2+ introduced the sentinel resolve-hostnames and sentinel announce-hostnames directives to address this.

In Kubernetes StatefulSets, the issue is particularly acute because IP addresses change on pod restarts, but service DNS names remain stable. Setting slave-announce-ip to the Kubernetes service name (e.g., redis-service.default.svc.cluster.local) is critical for proper failover behavior.

For cloud-hosted Redis (AWS ElastiCache, Azure Cache, DigitalOcean, etc.), the endpoint is already a resolvable hostname managed by the provider—ensure your security groups/network rules allow outbound DNS and port 6379 connections.

If using TLS/SSL connections to Redis, also verify that the hostname in the certificate matches the hostname you're connecting to, as certificate validation will fail on hostname mismatch.

Frequently asked questions

What does "ERR Failed to resolve hostname" mean?
When Redis tries to connect to a host specified by name (rather than IP address), it uses DNS to resolve that hostname to an IP address. If DNS lookup fails—whether due to misconfiguration, network issues, or an invalid hostname—Redis will return this error. This commonly occurs in Redis Sentinel deployments, cluster setups, or when connecting through intermediate services.
How do I fix "ERR Failed to resolve hostname"?
The "ERR Failed to resolve hostname" error occurs when Redis or a Redis client cannot resolve a hostname to its IP address through DNS. This is typically caused by DNS configuration issues, network connectivity problems, or incorrect hostname configuration.
What causes "ERR Failed to resolve hostname"?
DNS server is unreachable or not responding to hostname resolution queries The hostname is misspelled or does not exist in DNS Network connectivity is blocked between the client and DNS servers (port 53)
Is the "ERR Failed to resolve hostname" error serious?
Yes. This is a high-severity error that usually blocks work until it is fixed, but the steps above resolve it.

Official resources & further reading