Why Can\'t My Docker Image Find My Go Package: A Solution to the \"Cannot Find Package\" Error

Docker with Go App: Resolving "Cannot Find Package" Error

When building a Docker image with a Go application, encountering the "cannot find package" error can be frustrating. Let's delve into the issue and provide a solution.

The error originates when the Dockerfile copies the project files to the image root directory without installing dependencies or building the binary correctly. This mismatch causes the system to search for a binary that doesn't exist in the intended location (/go/bin/myapp).

To resolve this, we recommend using a Dockerfile structure like the following:

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 Dockerfile will:

1. Copy project files to /go/src/myapp.
2. Set the working directory to /go/src/myapp.
3. Install dependencies using go get (or your preferred dependency management tool).
4. Build and install the binary.
5. Set the entry point to the built binary.

To further debug the issue, you can use docker exec to run ls or any other command. For example:

docker exec <image name/hash> ls

Additionally, you can enter the shell in the generated image using:

docker run --rm -it <image hash/name> /bin/sh

This allows you to explore the image and gain a deeper understanding of its structure.

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