Learn how to fix the Redis Sentinel failed to resolve hostname error. Our Redis Support team is here to help you with your questions and concerns.

How to Fix ‘Redis Sentinel Failed to Resolve Hostname’ Issues

Did you know that this error usually occurs due to issues in resolving the provided hostname for the Redis Sentinel service?

Redis Sentinel failed to resolve hostname

Redis Sentinel ensures high availability for Redis. Hence, it needs to correctly resolve hostnames to identify and communicate with the appropriate servers.

Possible Causes

1. The hostname provided might be incorrect or misspelled.
2. Network problems like DNS issues, firewall rules, routing problems, or overall network outages can prevent the resolution of the hostname.
3. Furthermore, mistakes in the configuration of Redis Sentinel itself can cause this issue.
4. Additionally, when using containers or virtualized environments, specific networking or configuration issues can be the cause.

Solutions

• First, verify the provided hostname. Check that that the server name is entered accurately and without typos.
• Then, use tools like `ping`, `traceroute`, or `nslookup` to test network connectivity and name resolution. Check if the instance can reach the server and that DNS is correctly resolving the hostname.

  For example:

  ping bobcares.com
traceroute bobcares.com
nslookup bobcares.com

• Also, examine the Redis and Redis Sentinel configurations. Check if they are set up properly according to best practices and your specific use case.
• Furthermore, if we are using Docker, Kubernetes, etc, check the specific settings related to networking and name resolution. Adjust these settings if necessary for Redis Sentinel to work correctly.
• Also, review the logs provided by Redis and the system. They offer more detailed information about the error.

Issue: Redis Sentinel Throws Error: “Can’t resolve master instance hostname.

Did you know that only Redis Sentinel versions above 6.2 can resolve hostnames?

However, this is not enabled by default. So, we have to add `sentinel resolve-hostnames yes` to `sentinel.conf` to enable this feature. For older versions, replace the hostname with an IP address.

# In sentinel.conf
sentinel resolve-hostnames yes


Issue: Redis Sentinel Docker Container Can’t Resolve Master Instance Hostname

Check if the `ALLOW_EMPTY_PASSWORD=yes` environment variable is set in the Redis configuration. Sometimes, Redis Sentinel will not load if Redis exits due to improperly configured password properties. Here is a sample Docker configuration:

redis:
image: bitnami/redis:latest
networks:
- private
volumes:
- ./tmp:/tmp
environment:
- ALLOW_EMPTY_PASSWORD=yes
redis-sentinel:
image: 'bitnami/redis-sentinel:latest'
depends_on:
- redis
environment:
- REDIS_MASTER_HOST=redis
ports:
- '26379:26379'
networks:
- private


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Conclusion

In brief, our Support Experts demonstrated how to fix the Redis Sentinel failed to resolve hostname error.