Do not use 'go get' for retrieving assets; use git, wget, curl, etc. instead

[umarcor]

Description of problem

• go get is NOT for retrieving assets, but for adding Go (build) dependencies.
• git, wget, curl, etc. might be used for retrieving assets.
• In this project, go get is used incorrectly for retrieving assets.
• Enabling go modules is broken because the testing infrastructure relies on go get downloading assets to specific locations. See https://github.com/kata-containers/kata-containers/blob/2.0-dev/ci/lib.sh#L17.
• Travis CI is passing because go modules are NOT being used.
• Some maintainers seem to think that go modules are properly supported just because go.mod files were added to the repo.

kata-containers/runtime#1911 (comment)
@bergwolf:
We should not use the new go get to download code or binary inside a go module directory, -- it would fetch the code and add it to your go.mod dependency. git clone is your friend ;)

Expected result

Running Travis CI with go modules enabled should be successful.

Actual result

• umarcor@1cc0749
• https://travis-ci.com/github/umarcor/kata-containers/jobs/392554689

Please, see kata-containers/runtime#1420 (comment).

Further information

• Migrate to go modules (deprecate 'vendor') runtime#1420
• Migration from 'go dep' to 'go mod' runtime#1331
• Update golang versions runtime#1338
• switch vendoring from dep to go modules #42
• wip: Move to Go modules runtime#1911

[jodh-intel]

If anyone wants to do this, step 1 is to grep -r "go get" and change each occurrence to use curl -sLO $URL instead (no wget please).

[ariel-adam]

We will leave this as a parent issue not assigned to anyone specific.

[umarcor]

@jodh-intel, last time I had a look at this, the problem was not replacing go get with curl|wget|git. That is rather easy, since it is a mechanical replacement. The actual problem is that all the scripts rely on assets being installed in some specific location in the GOPATH. That location changes when go modules are enabled; so the scripts cannot find them. Installing assets into the GOPATH without using go is likely to produce more headaches than help solve the issue. Please, see the detailed explanation in kata-containers/runtime#1420 (comment) about the problems derived from just changing from go get to curl.

Therefore, three things need to be modified at the same time: how are assets retrieved, where are assets downloaded to, how do scripts find assets (sometimes hardcoded). I could and can "fix" the two first points, but the latter requires an expertise/knowledge about this project's testing infrastructure as a whole. As a result, I believe that modifying this needs to be guided by someone with a good understanding of the organisation and the overall testing architecture. I wouldn't call this a "good first issue".

[liubin]

This should be closed via kata-containers/tests#5224