Fix and optimize generator Docker image building (#1045)

* Fix Docker image of generator always pointing to latest tag

* new `REPO_TAG` variable can be used to specify the tag/branch to use for a build
* the Makefile default is to use the branch of the current repository `HEAD`
* the Dockerfile default (if building manually with Docker) is `main`
* updated CircleCI configuration to apply the correct `REPO_TAG` values

Signed-off-by: Hugo Hromic <[email protected]>

* Optimize Docker image of generator

* use multi-stage build to reduce final image size
* ensure to use the same Debian version (`bookworm`) for the builder and final images
* use `--no-install-recommends` to reduce unnecessary dependency downloads
* removed unnecessary `unzip` dependency in the image
* use modern syntax (using equal sign) for `ENV` Dockerfile directive

Signed-off-by: Hugo Hromic <[email protected]>

---------

Signed-off-by: Hugo Hromic <[email protected]>

.circleci/config.yml

@@ -53,8 +53,8 @@ jobs:
     steps:
     - prometheus/setup_build_environment:
         docker_version: ""
-    - run: make -C generator docker DOCKER_IMAGE_TAG=main
-    - run: make -C generator docker DOCKER_REPO=quay.io/prometheus DOCKER_IMAGE_TAG=main
+    - run: make -C generator docker REPO_TAG=main DOCKER_IMAGE_TAG=main
+    - run: make -C generator docker REPO_TAG=main DOCKER_REPO=quay.io/prometheus DOCKER_IMAGE_TAG=main
     - run: docker images
     - run: docker login -u $DOCKER_LOGIN -p $DOCKER_PASSWORD
     - run: docker login -u $QUAY_LOGIN -p $QUAY_PASSWORD quay.io
@@ -67,8 +67,8 @@ jobs:
     steps:
     - prometheus/setup_build_environment:
         docker_version: ""
-    - run: make -C generator docker DOCKER_IMAGE_TAG=$CIRCLE_TAG
-    - run: make -C generator docker DOCKER_IMAGE_TAG=$CIRCLE_TAG DOCKER_REPO=quay.io/prometheus
+    - run: make -C generator docker REPO_TAG=$CIRCLE_TAG DOCKER_IMAGE_TAG=$CIRCLE_TAG
+    - run: make -C generator docker REPO_TAG=$CIRCLE_TAG DOCKER_IMAGE_TAG=$CIRCLE_TAG DOCKER_REPO=quay.io/prometheus
     - run: docker login -u $DOCKER_LOGIN -p $DOCKER_PASSWORD
     - run: docker login -u $QUAY_LOGIN -p $QUAY_PASSWORD quay.io
     - run: |

generator/Dockerfile

@@ -1,13 +1,23 @@
-FROM golang:latest
+FROM golang:bookworm AS builder
 
-RUN apt-get update && \
-    apt-get install -y libsnmp-dev unzip && \
-    go install github.com/prometheus/snmp_exporter/generator@latest
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libsnmp-dev
+
+ARG REPO_TAG=main
+RUN go install github.com/prometheus/snmp_exporter/generator@"$REPO_TAG"
+
+FROM debian:bookworm-slim
 
 WORKDIR "/opt"
 
-ENTRYPOINT ["/go/bin/generator"]
+ENTRYPOINT ["/bin/generator"]
 
-ENV MIBDIRS mibs
+ENV MIBDIRS=mibs
 
 CMD ["generate"]
+
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends libsnmp40 \
+    && rm -rf /var/lib/apt/lists/*
+
+COPY --from=builder /go/bin/generator /bin/generator

generator/Makefile

@@ -16,8 +16,10 @@ MIB_PATH := 'mibs'
 
 CURL_OPTS ?= -L --no-progress-meter --retry 3 --retry-delay 3 --fail
 
+REPO_TAG ?= $(shell git rev-parse --abbrev-ref HEAD)
+
 DOCKER_IMAGE_NAME ?= snmp-generator
-DOCKER_IMAGE_TAG  ?= $(subst /,-,$(shell git rev-parse --abbrev-ref HEAD))
+DOCKER_IMAGE_TAG  ?= $(subst /,-,$(REPO_TAG))
 DOCKER_REPO       ?= prom
 
 SANITIZED_DOCKER_IMAGE_TAG := $(subst +,-,$(DOCKER_IMAGE_TAG))
@@ -79,7 +81,7 @@ parse_errors: generator mibs
 
 .PHONY: docker
 docker:
-	docker build -t "$(DOCKER_REPO)/$(DOCKER_IMAGE_NAME):$(SANITIZED_DOCKER_IMAGE_TAG)" .
+	docker build --build-arg REPO_TAG="$(REPO_TAG)" -t "$(DOCKER_REPO)/$(DOCKER_IMAGE_NAME):$(SANITIZED_DOCKER_IMAGE_TAG)" .
 
 .PHONY: docker-generate
 docker-generate: docker mibs