Скачать или смотреть Troubleshooting Container Communication across Different Hosts with Docker

Learn how to enable seamless communication between Docker containers on different hosts, and troubleshoot common connectivity issues with MySQL and Zabbix.
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This video is based on the question https://stackoverflow.com/q/63306290/ asked by the user 'Prasad27' ( https://stackoverflow.com/u/2189694/ ) and on the answer https://stackoverflow.com/a/63316623/ provided by the user 'Neo Anderson' ( https://stackoverflow.com/u/13736525/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Container Communication across Different Hosts with Docker

In the world of containers, communication between them is vital for many applications. However, when containers are hosted on different physical servers, like in your case, connectivity issues often arise. Let's address the problem of connecting a MySQL server running in a Docker container on one server to a Zabbix front-end container running on another server.

The Problem

You're working with two CentOS 8 servers. On Server 1, there is a MySQL server container, while on Server 2, you have a Zabbix front-end container (named zabbixfrontend). Your objective is to connect the Zabbix container to the MySQL server. However, you are encountering errors like:

[[See Video to Reveal this Text or Code Snippet]]

And attempts to check connectivity using nc (Netcat) return the message:

[[See Video to Reveal this Text or Code Snippet]]

This indicates that the Zabbix container cannot communicate with the MySQL server container across the two hosts.

Understanding the Issue

The connectivity challenge arises from how Docker handles networking for containers. When you deploy a container in the default bridge network mode, it receives an IP address from a specific subnet (e.g., 172.18.0.0/16), which is different from your MySQL server's subnet (e.g., 10.0.0.0/16). This situation leads to the "No route to host" error when you try to access the MySQL server from the Zabbix container.

Suggested Solution: Using Host Network Mode

A viable solution to this issue is to run your Zabbix container in the host network mode, which allows the container to directly use the host's networking stack. This way, you avoid issues related to disparate subnets. Here are the detailed steps to implement this solution:

Modify Your Docker Compose File

Update your docker-compose.yml by changing the networking mode for your Zabbix container to host. Remove the ports section, as it is unnecessary when using host mode. Here’s how your Docker Compose configuration should look:

[[See Video to Reveal this Text or Code Snippet]]

Accessing the Zabbix Web Interface

Once you deploy the Zabbix container in host mode, you can access the web interface directly from your host's IP:

For HTTP: http://localhost:8080

For HTTPS: https://localhost:8443

Important Considerations

While using the host network simplifies container communication across different servers, it's crucial to note that this approach may expose your applications directly to the host's network. Here are some factors to keep in mind:

Security: Since the service can be accessed through the host's IP, ensure proper security measures are in place, such as firewalls or access control lists (ACLs).

Port Conflicts: Ensure there are no other services running on the ports you access to avoid conflicts.

Conclusion

By utilizing the host network mode in your Docker setup, you can resolve the connectivity issues between your MySQL and Zabbix containers across different hosts. This approach is particularly useful in special setups like yours, where multiple independent Docker hosts are involved. Remember to weigh the benefits and risks of this configuration regarding security and accessibility. Happy containerizing!