How to solve the problem that the docker container cannot connect to the host database

With the rapid development of cloud computing, big data, artificial intelligence and other technologies, containerization technology has gradually become a very important part of enterprise projects, because the lightweight and rapid deployment of containers can effectively improve development efficiency. Shorten delivery cycle and reduce costs. However, in the process of using container technology, we often encounter some problems. One of the typical problems is that the container cannot connect to the host database.

1. Problem Description

When using containerization technology for project development, it is usually necessary to interact with the host's database. But sometimes, we find that the container cannot connect to the host database, causing the project to fail to run normally. In this case, we need to conduct in-depth analysis and troubleshooting of the network communication between the container and the host.

2. Possible reasons

2.1. IP address mismatch

The application in the container and the application on the host need to be connected through the network For communication, you need to assign an IP address to the container. Normally, the IP address inside the container is assigned by Docker, and this IP address is different from the host's IP address. Therefore, if we reference the IP address of the host machine instead of the IP address inside the container in the application, the connection will fail.

2.2. Incorrect port mapping

When network communication between the container and the host needs to be achieved through port mapping, if the mapping settings are incorrect, the connection will fail. For example, if we map the port inside the container to the port on the host, and the port number inside the container is referenced in the application instead of the port number on the host, the connection will fail.

2.3. Firewall blocking

Sometimes, we set access control rules on the firewall, which may cause the container to be unable to connect to the host database. For example, if we set the firewall to allow only the local machine to access a database, and the container is not on the local machine, the connection will fail.

3. Solution

For the problem that the container cannot connect to the host database, we can adopt the following solution:

3.1. Modify the application code

In the application, change the IP address and port number connecting to the database to the IP address and port number inside the container, so that you can successfully connect to the host database.

3.2. Modify the container’s network configuration

If the problem is caused by IP address mismatch, we can solve it by modifying the container’s network configuration. The specific method is: first find the IP address of the container, and then change the connection IP address in the application to the IP address of the container. In addition, we can also set the container's network to the host's network, which makes network communication between the container and the host easier.

3.3. Set the correct port mapping

If the problem is caused by incorrect port mapping settings, we can reset the port mapping to ensure that the ports inside the container can be correctly mapped to the host on the host's port.

3.4. Configure firewall rules

Finally, if the problem is caused by firewall blocking, we can set rules on the firewall that allow the container to access the database, so that the container can successfully connect to the host. The host's database.

4. Summary

The inability of the container to connect to the host database is a common problem when using containerization technology, but through in-depth analysis and troubleshooting, we can find the root cause of the problem and Take appropriate solutions. In daily development work, we must always pay attention to the network communication between the container and the host to ensure that the project can run normally, thereby improving development efficiency, shortening the delivery cycle, and reducing costs.

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