ci: Replace docker build args with secret mounts

ci/container-image-build-task.yml

@@ -24,7 +24,7 @@ params:
   CONTEXT: source/((flavor))
   IMAGE_PLATFORM: ((target-platform)) # This param tells the `concourse-oci-build-task` task which architecture to build the image for.
   BUILD_ARG_TARGETPLATFORM: ((target-platform)) # the instana-agent-docker Dockerfile requires a TARGETPLATFORM build arg.
-  BUILD_ARG_DOWNLOAD_KEY: ((agent-download-key)) # required by the instana-agent-docker Dockerfile
+  BUILDKIT_SECRETTEXT_DOWNLOAD_KEY: ((agent-download-key)) # required by the instana-agent-docker Dockerfile
   BUILD_ARG_FLAVOR: ((flavor)) # required by the instana-agent-docker Dockerfile
   BUILD_ARG_CLASSIFIER: ((classifier)) # required by the instana-agent-docker Dockerfile
   BUILD_ARG_VERSION: ((version)) # required by the instana-agent-docker Dockerfile

dynamic/Dockerfile

@@ -46,11 +46,11 @@ FROM registry.access.redhat.com/ubi8/ubi-minimal:latest AS instana-agent
 
 ARG TARGETPLATFORM='linux/amd64'
 ARG CLASSIFIER=''
-ARG DOWNLOAD_KEY
 # This is for backwards compatibility for end users that build their own images
 ARG FTP_PROXY
 
-RUN microdnf update && curl -sSL https://packages.instana.io/Instana.gpg -o /tmp/Instana.gpg && \
+RUN --mount=type=secret,id=DOWNLOAD_KEY DOWNLOAD_KEY="$(cat /run/secrets/DOWNLOAD_KEY)" && \
+    microdnf update && curl -sSL https://packages.instana.io/Instana.gpg -o /tmp/Instana.gpg && \
     rpm --import /tmp/Instana.gpg && \
     export arch=$(case "${TARGETPLATFORM}" in 'linux/amd64') echo 'x86_64' ;; 'linux/arm64') echo 'aarch64' ;; 'linux/s390x') echo 's390x' ;; 'linux/ppc64le') echo 'ppc64le' ;; esac) && \
     [[ -z "${FTP_PROXY}" ]] || DOWNLOAD_KEY="${FTP_PROXY}" && \

dynamic/README.md

@@ -18,12 +18,16 @@ features](https://github.com/docker/cli/blob/master/experimental/README.md) need
 export TARGETPLATFORM=linux/s390x
 export DOWNLOAD_KEY=my-key
 
+echo "${DOWNLOAD_KEY}" > ${HOME}/.INSTANA_DOWNLOAD_KEY
+
 docker buildx build --no-cache \
-  --build-arg DOWNLOAD_KEY="${DOWNLOAD_KEY}" \
+  --secret id=DOWNLOAD_KEY,src=${HOME}/.INSTANA_DOWNLOAD_KEY \
   --platform="${TARGETPLATFORM}" \
   --build-arg "TARGETPLATFORM=${TARGETPLATFORM}" \
   -t instana/agent \
   .
+
+rm -f ${HOME}/.INSTANA_DOWNLOAD_KEY
 ```
 
 Supported values of `<PLATFORM>`:

static/Dockerfile

@@ -46,11 +46,12 @@ FROM registry.access.redhat.com/ubi8/ubi-minimal:latest AS instana-agent
 
 ARG TARGETPLATFORM='linux/amd64'
 ARG CLASSIFIER=''
-ARG DOWNLOAD_KEY
 # This is for backwards compatibility for end users that build their own images
 ARG FTP_PROXY
 
-RUN microdnf update && curl -sSL https://packages.instana.io/Instana.gpg -o /tmp/Instana.gpg && \
+# Use secret mounts to prevent leakage of secrets in docker image metadata
+RUN --mount=type=secret,id=DOWNLOAD_KEY DOWNLOAD_KEY="$(cat /run/secrets/DOWNLOAD_KEY)" && \
+    microdnf update && curl -sSL https://packages.instana.io/Instana.gpg -o /tmp/Instana.gpg && \
     rpm --import /tmp/Instana.gpg && \
     export arch=$(case "${TARGETPLATFORM}" in 'linux/amd64') echo 'x86_64' ;; 'linux/arm64') echo 'aarch64' ;; 'linux/s390x') echo 's390x' ;; 'linux/ppc64le') echo 'ppc64le' ;; esac) && \
     [[ -z "${FTP_PROXY}" ]] || DOWNLOAD_KEY="${FTP_PROXY}" && \

static/README.md

@@ -12,12 +12,16 @@ features](https://github.com/docker/cli/blob/master/experimental/README.md) need
 export TARGETPLATFORM=linux/s390x
 export DOWNLOAD_KEY=my-key
 
+echo "${DOWNLOAD_KEY}" > ${HOME}/.INSTANA_DOWNLOAD_KEY
+
 docker buildx build --no-cache \
-  --build-arg DOWNLOAD_KEY="${DOWNLOAD_KEY}" \
+  --secret id=DOWNLOAD_KEY,src=${HOME}/.INSTANA_DOWNLOAD_KEY \
   --platform="${TARGETPLATFORM}" \
   --build-arg "TARGETPLATFORM=${TARGETPLATFORM}" \
   -t containers.instana.io/instana/release/agent/static \
   .
+
+rm -f ~/.INSTANA_DOWNLOAD_KEY
 ```
 
 Supported values of `<PLATFORM>`: