I want to build a tiny container image from scratch using Buildah to run a Go app. Apart from the app itself, what other libraries etc need to be included. I am thinking that glibc is needed - is there anything else?
So in summary, I think I am asking "what are all the external dependencies that a compiled Go app needs on Linux?"
@Dave C gave the information to correctly answer this. Using ldd with the test app returned:
[bryon@localhost resttest]$ ldd restest
linux-vdso.so.1 (0x00007fff139fe000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007fbad6ce2000)
libc.so.6 => /lib64/libc.so.6 (0x00007fbad691f000)
/lib64/ld-linux-x86-64.so.2 (0x00007fbad6f02000)
[bryon@localhost resttest]$
So for those looking to build a minimal container with Buildah, the BASH script to generate it would look like this:
#!/bin/bash
#
# Run this shell script after you have run the command: "buildah unshare"
#
git clone https://github.com/bryonbaker/resttest.git
cd resttest
go build restest.go
container=$(buildah from scratch)
mnt=$(buildah mount $container)
mkdir $mnt/bin
mkdir $mnt/lib64
buildah config --workingdir /bin $container
buildah copy $container restest /bin/restest
buildah copy $container /lib64/libpthread.so.0 /lib64
buildah copy $container /lib64/libc.so.6 /lib64
buildah copy $container /lib64/ld-linux-x86-64.so.2 /lib64
buildah config --port 8000 $container
#
# This step is not working properly.
# Need to run with podman -p 8000:8000 --entrypoint /bin/restest restest:latest
buildah config --entrypoint /bin/restest $container
buildah commit --format docker $container restest:latest
This generates a 14MB container for a simple microservice! There are no additional files to be worrying about for vulnerabilities etc.
I have a small defect I can't work out on entrypoints so I am overriding the entrypoint on start, but to test it run:
podman -p8000:8000 --entrypoint /bin/restest restest:latest
Then just type the following in a Terminal session:
curl http://localhost:8000
So thanks Dave C!
I am assuming you have included the app dependencies in your docker image.
You won't require any external dependency to build a docker image. Just base image from Go is sufficient to build and run on Linux machines.
# Start from the latest Go base image
FROM golang:latest
# Set the Current Working Directory inside the container
WORKDIR /app
# Copy go mod and sum files
COPY go.mod go.sum ./
# Download all dependencies. Dependencies will be cached if the go.mod and go.sum files are not changed
RUN go mod download