From 3db843d4fb898e454fb6c6618fceef351c695871 Mon Sep 17 00:00:00 2001
From: Ludovic Muller <ludovicmuller1@gmail.com>
Date: Mon, 24 Jun 2024 17:12:19 +0200
Subject: [PATCH] feat: enable Prometheus exporter

---
 .changeset/fair-games-rule.md |  5 +++++
 Dockerfile                    | 21 ++++++++++++++++++++-
 README.md                     |  2 ++
 entrypoint.sh                 |  8 ++++++++
 4 files changed, 35 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/fair-games-rule.md

diff --git a/.changeset/fair-games-rule.md b/.changeset/fair-games-rule.md
new file mode 100644
index 0000000..e13da4a
--- /dev/null
+++ b/.changeset/fair-games-rule.md
@@ -0,0 +1,5 @@
+---
+"varnish-post": minor
+---
+
+Enable Prometheus Exporter by setting `ENABLE_PROMETHEUS_EXPORTER` to `true`.
diff --git a/Dockerfile b/Dockerfile
index a42b373..3ee9b4b 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,3 +1,16 @@
+# Build the prometheus_varnish_exporter binary
+FROM docker.io/library/golang:1.22 as prometheus_varnish_exporter
+WORKDIR /app
+
+# Releases: https://github.com/jonnenauha/prometheus_varnish_exporter/releases
+ARG PROMETHEUS_VARNISH_EXPORTER_VERSION=1.6.1
+
+RUN git clone https://github.com/jonnenauha/prometheus_varnish_exporter.git . \
+  && git checkout "${PROMETHEUS_VARNISH_EXPORTER_VERSION}" \
+  && go mod download \
+  && go build -o prometheus_varnish_exporter
+
+# Build the final image
 FROM docker.io/library/ubuntu:22.04
 
 # Configuration
@@ -11,6 +24,7 @@ ENV DISABLE_ERROR_CACHING="true"
 ENV DISABLE_ERROR_CACHING_TTL="30s"
 ENV CONFIG_FILE="default.vcl"
 ENV ENABLE_LOGS="true"
+ENV ENABLE_PROMETHEUS_EXPORTER="false"
 
 # Install some dependencies
 RUN apt-get update \
@@ -21,11 +35,16 @@ RUN apt-get update \
   varnish-modules \
   && apt-get clean
 
+# Get the prometheus_varnish_exporter binary
+COPY --from=prometheus_varnish_exporter \
+  /app/prometheus_varnish_exporter \
+  /usr/local/bin/prometheus_varnish_exporter
+
 # Deploy our custom configuration
 WORKDIR /etc/varnish
 COPY config/ /templates
 COPY entrypoint.sh /
 RUN chmod +x /entrypoint.sh
 
-EXPOSE 80 8443
+EXPOSE 80 8443 9131
 ENTRYPOINT [ "tini", "--", "/entrypoint.sh" ]
diff --git a/README.md b/README.md
index d1c9463..152c91e 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,8 @@ You can use following environment variables for configuration:
 - `DISABLE_ERROR_CACHING_TTL`: time where requests should be directly sent to the backend after an error occured (default: `30s`)
 - `CONFIG_FILE`: the name of the configuration file to use (default: `default.vcl`)
 - `ENABLE_LOGS`: enable logs (default: `true`)
+- `ENABLE_PROMETHEUS_EXPORTER`: enable the Prometheus exporter if set to `true` (default: `false`).
+  If enabled, the exporter will be available on the 9131 port.
 
 ## Cache invalidation
 
diff --git a/entrypoint.sh b/entrypoint.sh
index b46ad1d..fd59bdf 100755
--- a/entrypoint.sh
+++ b/entrypoint.sh
@@ -1,6 +1,7 @@
 #!/bin/sh
 
 ENABLE_LOGS="${ENABLE_LOGS}"
+ENABLE_PROMETHEUS_EXPORTER="${ENABLE_PROMETHEUS_EXPORTER}"
 
 set -eu
 
@@ -18,6 +19,13 @@ if [ "${ENABLE_LOGS}" = "true" ]; then
   varnishncsa&
 fi
 
+# Start prometheus_varnish_exporter if enabled
+if [ "${ENABLE_PROMETHEUS_EXPORTER}" = "true" ]; then
+  (sleep 2 && prometheus_varnish_exporter \
+    -web.listen-address ":9131" \
+    -web.telemetry-path "/metrics") &
+fi
+
 set -x
 
 # Run Varnish