Learn how to fix the HAProxy Docker Could not resolve address error. Our HAProxy Support team is here to help you with your questions and concerns.

HAProxy Docker Could not resolve address | Troubleshooting

If you have been coming across the following error, message, you have come to the right place.

Could not resolve address

According to our experts, this error occurs when HAProxy cannot resolve the hostname or IP address of a backend server or service that it is configured to connect to.

Let’s take a look at the potential causes and how to solve them.

Troubleshooting Tips

• To begin with, check the backend server configuration in the HAProxy configuration file. In other words, make sure the backend server’s hostname or IP address is correct. If we are using DNS names, they have to be resolvable from the Docker container.

  This can be done by adding a resolvers section to the haproxy cfg after the “defaults” section:

  resolvers docker parse-resolv-conf

  Furthermore, we have to set the haproxy to not confirm backend addresses on startup. This is because the container hostname to address resolution might not be set up yet.
• Next, we have to verify that the Docker container running HAProxy can resolve DNS names and connect to external hosts.
• If we use DNS names for backend server addresses, the DNS server configured in the Docker container can resolve the hostname to an IP address. We can test DNS resolution within the container with tools like nslookup or dig.
• Then, check if there are any custom DNS configurations required for the Docker container. The DNS resolution has to be correct.
• If the error still exists, check if any firewall rules or network restrictions are blocking outgoing connections from the Docker container.
• Sometimes, restarting the Docker networking stack or restarting the Docker daemon can resolve DNS resolution issues.
• Finally, use debugging tools like ping, traceroute, or curl, to troubleshoot network connectivity and DNS resolution.

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Conclusion

In brief, our Support Experts demonstrated how to resolve the HAProxy Docker Could not resolve address error.