What should I do if the docker container cannot connect to the local database?

In the process of using Docker containers, it often involves linking to the database on the host. However, sometimes when trying to connect to the local database, the connection fails. This article will explain why this might happen and provide some solutions.

1. Problem description

In the process of using Docker containers, sometimes it is necessary to link the application in the container with the database on the host. In some cases, we can connect through the IP address of the container and the IP address of the host, but sometimes this method does not successfully connect. For example, when using a Docker container to install a database such as MySQL, the application in the container cannot link to the MySQL database on the host.

2. Cause of the problem

1. The host and container networks are not interoperable

If the host and container use different networks, the communication between the two is not interoperable. of. In this case, the container cannot link to the database on the host.

2. The host IP address changes

When the host's IP address changes, the address linking to the local database in the container also needs to be modified accordingly. Otherwise, the container will not be able to link to the current host's database.

3. Database permission issues

In some cases, the database on the host does not have permission to open remote connections and only allows local connections. At this time, the application in the container cannot connect to the database.

3. Solution

1. Use Docker’s host network

When creating a Docker container, you can use --net=host to specify the network used by the host. . In this way, the application in the container and the database on the host are on the same network and can communicate with each other.

2. Using Docker's bridge network

Using Docker's bridge network can connect the network used by the container and the host to each other. When creating a Docker container, use the parameter --link to specify the connection to the local database.

3. Modify the host IP address

If the host IP address changes, the address connecting to the local database in the container also needs to be modified. The easiest way is to use a host alias in the container to connect to the database on the host instead of using the host IP address. You can use the host name or localhost instead of the host IP address to connect.

4. Modify database permissions

If there is a database permission problem, it can be solved by modifying the database permissions. In a MySQL database, you can use the GRANT statement to grant permissions to remote connections.

4. Summary

When using a Docker container to link to the database on the host, the link may fail. This situation may be caused by the host and container networks not communicating, the host IP address changing, or database permission issues. These problems can be solved by using Docker's host network and bridge network, modifying the host IP address, and modifying database permissions.

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