ci,makefile: add hadolint Dockerfile linting

.drone.yml

@@ -8,6 +8,21 @@ platform:
   arch: amd64
 
 steps:
+- name: hadolint
+  pull: always
+  image: hadolint/hadolint:v1.23.0-8-gb01c5a9-alpine
+  commands:
+  - hadolint --version
+  - hadolint Dockerfile
+  when:
+    ref:
+    - refs/heads/dev
+    - "refs/heads/feature-**"
+    - "refs/pull/**"
+    - "refs/tags/**"
+    event:
+      exclude: [cron]
+
 - name: kaniko-build
   pull: always
   image: immawanderer/drone-kaniko:linux-amd64

.hadolint.yaml

@@ -0,0 +1,10 @@
+ignored:
+  # DL3039 error: Do not use dnf update.
+  # image is nightly updated
+  - DL3039
+  # DL3041 warning: Specify version with `dnf install -y <package>-<version>`.
+  - DL3041
+  # SC2039 warning: In POSIX sh, brace expansion is undefined.
+  # it actually still works
+  - SC2039
+

Makefile

@@ -9,8 +9,13 @@ kanikoexecutorimg = gcr.io/kaniko-project/executor:debug
 kanikowdir = /src
 kanikocontext = .
 kanikoargs = -f=$(dfile) -c=$(kanikocontext) --use-new-run --snapshotMode=redo --no-push --force
+hadolintimg = hadolint/hadolint:v1.23.0-8-gb01c5a9-alpine
+hadolintargs = run --rm -i -v $$PWD/.hadolint.yaml:/root/.config/hadolint.yaml
 
-.PHONY: build kaniko clean test prune
+.PHONY: hadolint build kaniko clean test prune
+
+hadolint:
+	$(dcmd) $(hadolintargs) $(hadolintimg) < $(dfile)
 
 kaniko:
 	$(dcmd) $(dargskaniko) $(kanikoexecutorimg) $(kanikoargs)
@@ -21,7 +26,7 @@ build:
 clean:
 	$(dcmd) $(cleanargs)
 
-test: build kaniko
+test: hadolint build kaniko
 
 prune:
 	$(dcmd) $(pruneargs)