Why Can't I Connect to My Go gRPC Server in a Docker Container?

Troubleshooting a GRPC Connection Error: "Cannot Connect to Go GRPC Server Running in Local Docker Container"

Issue:

When attempting to connect to a Go GRPC server running within a Docker container, the error "transport: http2Client.notifyError got notified that the client transport was broken EOF. FATA[0000] rpc error: code = Internal desc = transport is closing" is encountered.

Explanation:

By default, GRPC servers listening on a localhost address ("127.0.0.1") are only accessible from within the same machine or container. When the server is run within a Docker container, it is given a separate IP address that cannot be accessed from outside the container.

Solution:

To resolve this issue, the GRPC server should be bound to a wildcard address (":51672") instead of "localhost:51672." This will allow the server to listen on all IP addresses associated with the container, making it accessible to clients outside of the container.

Docker Networking:

When exposing a port (51672 in this case) in a Docker container, Docker creates iptables rules to forward incoming traffic from the host machine's IP address (127.0.0.1) to the container's internal IP address. However, if the server is listening on "localhost:51672," it will only be accessible from within the container, not from the host machine.

Additional Information:

• Exposing a port in a Docker container using "-p" maps the container's internal IP address to the host machine's IP address.
• The iptables rules created by Docker can be viewed using the commands "iptables -n -L" and "iptables -t nat -n -L."

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