Startup message can have blank version

[bboreham]

I see this at the top of my logs:

caller=main.go:68 msg="Starting Cortex" version="(version=, branch=, revision=)"

I guess something is supposed to put a value into those strings?
Maybe we would consider this approach, new with Go Modules: https://github.com/dlespiau/go-main-module-version

This is running image cortexproject/cortex:master-de231804 from Dockerhub.

[ariefrahmansyah]

Hi, I would like to pick this up. I have two solutions in mind:

Proposed solution 1: We still use the current approach and fix missing value.

From my understanding, the current code is using Prometheus' common version package and we can use -ldflags to set these build information value. We can put it on Makefile and it will be something like this:

VERSION=$(shell cat VERSION)
GIT_REVISION=$(shell git rev-parse HEAD)
GIT_BRANCH=$(shell git rev-parse --abbrev-ref HEAD)

GO_BUILD_FLAGS := -X github.com/cortexproject/cortex/vendor/github.com/prometheus/common/version.Version=${VERSION} \
        -X github.com/cortexproject/cortex/vendor/github.com/prometheus/common/version.Revision=${GIT_REVISION} \
        -X github.com/cortexproject/cortex/vendor/github.com/prometheus/common/version.Branch=${GIT_BRANCH}

GO_FLAGS := -ldflags "${GO_BUILD_FLAGS} -extldflags \"-static\" -s -w" -tags netgo

$(EXES):
	CGO_ENABLED=0 go build $(GO_FLAGS) -o $@ ./$(@D)
	$(NETGO_CHECK)

Proposed solution 2: Read Build Information from inside the code.

We can use your proposed approach here by using:

1. ReadBuildInfo as we can see on https://github.com/dlespiau/go-main-module-version
2. Execute git command using exec.Command() as we can see on https://github.com/prometheus/promu/blob/master/pkg/repository/info.go

---

Personally, I prefer to use solution 1. Even though Prometheus' common package is made to be shared across Prometheus components and libraries, the version package itself is generic enough to be used by other projects. Another benefit is we don't need to modify any Cortex Golang code.

[bboreham]

Please go ahead, @ariefrahmansyah

We have a script https://github.com/cortexproject/cortex/blob/master/tools/image-tag which adds a -WIP suffix when there are local modifications to the git tree - that can be useful.

Separately, I think the raw VERSION file is worse than nothing, since it is wrong on every commit but one per release.

[bboreham]

Also it would be good to add the version to metric cortex_build_info