build: fix the image to work with golangci-lint

In #195 I updated the Go version, and also swapped from Debian to Alpine for
the base image. This was OK for the build, but it turns out we also use the
same image to run golangci-lint. That action uses a binary for a different
architecture, which fails on this image.

So:
- Keep the Go version, but revert the base image.
- Add some documentation to the workflow configs.

.github/workflows/ci.yml

@@ -14,6 +14,9 @@ jobs:
     if: "!startsWith(github.ref, 'refs/tags/') && github.ref != 'refs/heads/master'"
 
   Test:
+    # The custom image here contains pre-built libraries for leveldb and
+    # rocksdb, which are needed to build and test those modules.
+    # To update the container image, see docker.yml.
     runs-on: ubuntu-latest
     container: tendermintdev/docker-tm-db-testing
     steps:

.github/workflows/docker.yml

@@ -1,3 +1,11 @@
+# This workflow builds and pushes a new version of the build container image
+# when the tools directory changes on master. Edit tools/Dockerfile.
+#
+# This workflow does not push a new image until it is merged, so tests that
+# depend on changes in this image will not pass until this workflow succeeds.
+# For that reason, changes here should be done in a separate PR in advance of
+# work that depends on them.
+
 name: Build & Push TM-DB-Testing
 on:
   pull_request:

.github/workflows/lint.yml

@@ -7,13 +7,17 @@ on:
 
 jobs:
   golangci:
+    # We need to run the linter on the same image we use for building, since it
+    # needs the C libraries installed for the dependencies to typecheck.
     runs-on: ubuntu-latest
     container: tendermintdev/docker-tm-db-testing
     steps:
       - uses: actions/checkout@v2
       - uses: golangci/golangci-lint-action@v2.5.2
         with:
-          # Required: the version of golangci-lint is required and must be specified without patch version: we always use the latest patch version.
+          # Required: the version of golangci-lint is required and must be
+          # specified without patch version: we always use the latest patch
+          # version.
           version: v1.30
           args: --timeout 10m
           github-token: ${{ secrets.github_token }}

tools/Dockerfile

@@ -1,4 +1,13 @@
-FROM golang:1.16-alpine
+# This file defines the container image used to build and test tm-db in CI.
+# The CI workflows use the latest tag of tendermintdev/docker-tm-db-testing
+# built from these settings.
+#
+# The jobs defined in the Build & Push workflow will build and update the image
+# when changes to this file are merged.  If you have other changes that require
+# updates here, merge the changes here first and let the image get updated (or
+# push a new version manually) before PRs that depend on them.
+
+FROM golang:1.17-alpine
 
 ENV LD_LIBRARY_PATH=/usr/local/lib