Why Does My Go Docker Build Fail with \'cannot find package\' Error?

Troubleshooting "cannot find package" Error in Docker Build for Go App

Building a Docker image with a Go application can sometimes result in the "cannot find package" error. To understand the cause and find a solution, let's examine the provided Dockerfile and the root cause of the issue.

The Dockerfile you provided copies all files to the root directory of the image, including your myapp folder. While this may seem correct, it actually creates a problem when attempting to build the Go application.

After copying the files, you run go build myapp. However, the Go compiler expects the application code to be present in the /go/src/myapp directory. Since you did not instruct the Dockerfile to install any dependencies or move the code to the expected location, it cannot find the myapp package and throws the error.

To resolve this issue, modify your Dockerfile as follows:

FROM golang:1.9.2
ADD . /go/src/myapp
WORKDIR /go/src/myapp
RUN go get myapp
RUN go install
ENTRYPOINT ["/go/bin/myapp"]

This modified Dockerfile will perform the following operations:

1. Copy project files to /go/src/myapp.
2. Set the working directory to /go/src/myapp.
3. Install dependencies using go get.
4. Install/build the binary using go install.
5. Set the entry point for the image.

By following these steps, your Dockerfile will correctly install and build the Go application, eliminating the "cannot find package" error.

Additional Troubleshooting Tips

If you still encounter issues, consider using docker exec to inspect the image's contents and diagnose the problem further. You can also enter the shell of the generated image to gain a better understanding of the environment.

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