Add Dockerfile for use in CI

[barakbd]

Ref: https://github.com/warrensbox/terraform-switcher/issues/109

Thank you to @hongkongkiwi for the Dockerfile code.

The simplest solution to automate build in Dockerfub is to link GitHub account and use Automated Builds. For more control, you may want to add docker build/push in Travis-ci.

You can see en example here: https://hub.docker.com/r/barakbd/tfswitch

[zot24]

As extra information in case that helps anyone, I have just learned the following while checking this PR:

We can't use as a base and minimal image scratch here because terraform-switcher use os/user and that thing is using a C system call internally to getpwuid_r which is not in scratch obviously, that's the reason why we are compiling this code with the env CGO_ENABLED=1 and therefore CGO_ENABLED=0 which is required to make your binary work on scratch base image won't work

source: https://stackoverflow.com/a/29899712

---

When trying to build a golang binary using the golang docker image, from a repo that's using go.mod you might get the following error:

$GOPATH/go.mod exists but should not

That's because on the golang docker image the $GOPATH it's set by default and go build doesn't know if it should use the local path where we are running the build command to download the dependencies or $GOPATH, so to solve this we have to unset the environment variable:

unset GOPATH

[barakbd]

I indeed see this issue with scratch:

$ docker run -it --rm tfswitch-scratch:multi -l      
2021/05/27 05:20:40 Error getting url: Get "https://releases.hashicorp.com/terraform/": x509: certificate signed by unknown authority
2021/05/27 05:20:40 user: Current requires cgo or $USER set in environment

The alpine based image is not much larger so it's fine:

$ docker images          
REPOSITORY         TAG       IMAGE ID       CREATED          SIZE
tfswitch-alpine    multi     e5d1a420880c   2 minutes ago    18.9MB
tfswitch-scratch   multi     67be03c96f40   10 minutes ago   13.3MB

[barakbd]

I updated to go 1.16 and as a consequence also had update vendor files with go mod vendor. AFAIK, it is ok to gitignore the vendor dir (https://stackoverflow.com/questions/51118691/should-i-add-go-dep-vendor-to-gitignore) but it is a matter of preference.

[barakbd]

Tested the docker image with a TF repo (running this from withtin a TF repo directory):

$ docker run -it --entrypoint sh --rm -v $PWD:/terraform tfswitch:latest 
/ # ls
bin        etc        lib        mnt        proc       run        srv        terraform  usr
dev        home       media      opt        root       sbin       sys        tmp        var
/ # cd terraform/
/terraform # tfswitch
Reading required version from terraform file
Reading required version from constraint: ~> 0.14.0
Matched version: 0.14.11
Downloading https://releases.hashicorp.com/terraform/0.14.11/terraform_0.14.11_linux_amd64.zip to terraform_0.14.11_linux_amd64.zip
Downloading ...
33789439 bytes downloaded.
Switched terraform to version "0.14.11" 
/terraform # ls
Jenkinsfile         config              iam.tf              output.tf           secrets-manager.tf  variables.tf
README.md           ecr.tf              lambda.tf           provider.tf         sqs.tf
api-gateway.tf      files               locals.tf           rds.tf              terraform.tf        vpc.tf

[barakbd]

@warrensbox - if you can remove the need for the os/user and then we can build with CGO_ENABLED=0 we can make the docker image tiny using FROM scratch

[barakbd]

Maybe we can do this here https://github.com/warrensbox/terraform-switcher/blob/a710b0368ae3aa13b0c4e1891ecce596e9e52c09/lib/install.go#L58:

if errCurr != nil {
    installLocation = '/' + installPath
}

Since scratch has only / as a path.

I am not too familiar with go so this is just a suggestion.

[warrensbox]

As extra information in case that helps anyone, I have just learned the following while checking this PR:

We can't use as a base and minimal image scratch here because terraform-switcher use os/user and that thing is using a C system call internally to getpwuid_r which is not in scratch obviously, that's the reason why we are compiling this code with the env CGO_ENABLED=1 and therefore CGO_ENABLED=0 which is required to make your binary work on scratch base image won't work

source: https://stackoverflow.com/a/29899712

When trying to build a golang binary using the golang docker image, from a repo that's using go.mod you might get the following error:

$GOPATH/go.mod exists but should not

That's because on the golang docker image the $GOPATH it's set by default and go build doesn't know if it should use the local path where we are running the build command to download the dependencies or $GOPATH, so to solve this we have to unset the environment variable:

unset GOPATH

We can try to use this library to avoid using cgo - https://github.com/mitchellh/go-homedir

[warrensbox]

Will close this for now. Please open a PR again with latest code if this is still needed.