Switch to Go 1.12 & replace dep by go mod

.circleci/config.yml

@@ -4,8 +4,10 @@ jobs:
   test:
     docker:
       # Available from https://hub.docker.com/r/circleci/golang/
-      - image: circleci/golang:1.10
+      - image: circleci/golang:1.12
     working_directory: /go/src/github.com/improbable-eng/thanos
+    environment:
+      GO111MODULE: 'on'
     steps:
       - checkout
       - setup_remote_docker:
@@ -19,7 +21,7 @@ jobs:
               echo $GOOGLE_APPLICATION_CREDENTIALS_CONTENT > /go/src/github.com/improbable-eng/thanos/circleci-gcs-creds.json
               echo "Awesome! GCS integration tests are enabled."
             fi
-      - run: make deps DEPARGS="-v"
+      - run: make check-go-mod
       - run: make errcheck
       - run: make check-docs
       - run: make format

.errcheck_excludes.txt

@@ -1,3 +1,3 @@
-(github.com/improbable-eng/thanos/vendor/github.com/go-kit/kit/log.Logger).Log
+(github.com/go-kit/kit/log.Logger).Log
 fmt.Fprintln
 fmt.Fprint

.gitignore

@@ -1,8 +1,6 @@
 /prometheus
 /thanos
 vendor/
-.dep-finished
-/.vendor-new
 
 # Ignore minikube setup working dirs.
 kube/bin

CONTRIBUTING.md

@@ -65,3 +65,25 @@ CI runs GCS and inmem tests only for now. Not having these variables will produc
 7. You may merge the Pull Request in once you have the sign-off of at least one developers with write access, or if you
    do not have permission to do that, you may request the second reviewer to merge it for you.
 8. If you feel like your PR waits too long for a review, feel free to ping [`#thanos-dev`](https://join.slack.com/t/improbable-eng/shared_invite/enQtMzQ1ODcyMzQ5MjM4LWY5ZWZmNGM2ODc5MmViNmQ3ZTA3ZTY3NzQwOTBlMTkzZmIxZTIxODk0OWU3YjZhNWVlNDU3MDlkZGViZjhkMjc) channel on our slack for review!
+
+## Dependency management
+
+The Thanos project uses [Go modules](https://golang.org/cmd/go/#hdr-Modules__module_versions__and_more) to manage dependencies on external packages. This requires a working Go environment with version 1.11 or greater, git and bzr installed.
+
+To add or update a new dependency, use the `go get` command:
+
+```bash
+# Pick the latest tagged release.
+go get example.com/some/module/pkg
+
+# Pick a specific version.
+go get example.com/some/module/pkg@vX.Y.Z
+```
+
+Tidy up the `go.mod` and `go.sum` files:
+
+```bash
+make vendor
+```
+
+You have to commit the changes to `go.mod` and `go.sum` before submitting the pull request.

Dockerfile.multi-stage

@@ -1,4 +1,4 @@
-FROM golang:1.11-alpine3.9 as builder
+FROM golang:1.12-alpine3.9 as builder
 
 ADD . $GOPATH/src/github.com/improbable-eng/thanos
 WORKDIR $GOPATH/src/github.com/improbable-eng/thanos