fix: Use values from user args when running Docker healthcheck

Signed-off-by: Vikas Shah <vikas.shah@ocado.com>

Author: vikas-shah

Dockerfile

@@ -6,8 +6,13 @@ LABEL maintainer="The Prometheus Authors <prometheus-developers@googlegroups.com
 ARG ARCH="amd64"
 ARG OS="linux"
 COPY .build/${OS}-${ARCH}/statsd_exporter /bin/statsd_exporter
+COPY docker-entrypoint.sh /bin/docker-entrypoint.sh
+RUN chmod +x /bin/docker-entrypoint.sh
+
+ENV TELEMETRY_PATH=/metrics \
+    LISTEN_PORT=9102
 
 USER        65534
 EXPOSE      9102 9125 9125/udp
-HEALTHCHECK CMD wget --spider -S "http://localhost:9102/metrics" -T 60 2>&1 || exit 1
-ENTRYPOINT  [ "/bin/statsd_exporter" ]
+HEALTHCHECK CMD if [ -r /tmp/statsd_exporter_healthcheck.env ]; then LISTEN_PORT="$(sed -n 's/^LISTEN_PORT=//p' /tmp/statsd_exporter_healthcheck.env | tail -n 1)"; TELEMETRY_PATH="$(sed -n 's/^TELEMETRY_PATH=//p' /tmp/statsd_exporter_healthcheck.env | tail -n 1)"; fi; wget --spider -S "http://localhost:${LISTEN_PORT:-9102}${TELEMETRY_PATH:-/metrics}" -T 60 2>&1 || exit 1
+ENTRYPOINT  [ "/bin/docker-entrypoint.sh" ]

README.md

@@ -520,6 +520,9 @@ docker run -d -p 9102:9102 -p 9125:9125 -p 9125:9125/udp \
         prom/statsd-exporter --statsd.mapping-config=/tmp/statsd_mapping.yml
 ```
 
+The container image healthcheck follows runtime values from `--web.telemetry-path` and 
+`--web.listen-address` (defaulting to `/metrics` and port `9102` when these flags are not provided).
+
 ## Library packages
 
 Parts of the implementation of this exporter are available as separate packages.

docker-entrypoint.sh

@@ -0,0 +1,76 @@
+#!/bin/sh
+
+set -eu
+
+HEALTHCHECK_ENV_FILE=/tmp/statsd_exporter_healthcheck.env
+STATSD_EXPORTER_BIN=${STATSD_EXPORTER_BIN:-/bin/statsd_exporter}
+
+telemetry_path="/metrics"
+listen_port="9102"
+listen_address=""
+pending_flag=""
+
+# Parse both formats --flag=value and --flag value forms without altering original args.
+for arg in "$@"; do
+    case "$pending_flag" in
+        telemetry_path)
+            telemetry_path="$arg"
+            pending_flag=""
+            continue
+            ;;
+        listen_address)
+            listen_address="$arg"
+            pending_flag=""
+            continue
+            ;;
+    esac
+
+    case "$arg" in
+        --web.telemetry-path=*)
+            telemetry_path=${arg#*=}
+            ;;
+        --web.telemetry-path)
+            pending_flag="telemetry_path"
+            ;;
+        --web.listen-address=*)
+            listen_address=${arg#*=}
+            ;;
+        --web.listen-address)
+            pending_flag="listen_address"
+            ;;
+    esac
+done
+
+# Ensure telemetry path is non-empty and absolute for URL construction.
+if [ -z "$telemetry_path" ]; then
+    telemetry_path="/metrics"
+elif [ "${telemetry_path#/}" = "$telemetry_path" ]; then
+    telemetry_path="/$telemetry_path"
+fi
+
+# Derive port from the final :PORT segment (works for host:port and [::]:port).
+if [ -n "$listen_address" ]; then
+    port_candidate=${listen_address##*:}
+    case "$port_candidate" in
+        ''|*[!0-9]*)
+            ;;
+        *)
+            if [ "$port_candidate" -ge 1 ] 2>/dev/null && [ "$port_candidate" -le 65535 ] 2>/dev/null; then
+                listen_port="$port_candidate"
+            fi
+            ;;
+    esac
+fi
+
+export TELEMETRY_PATH="$telemetry_path"
+export LISTEN_PORT="$listen_port"
+
+# Persist parsed values so Docker healthcheck invocations can read them later.
+tmp_env_file="${HEALTHCHECK_ENV_FILE}.tmp"
+{
+    printf 'TELEMETRY_PATH=%s\n' "$TELEMETRY_PATH"
+    printf 'LISTEN_PORT=%s\n' "$LISTEN_PORT"
+} >"$tmp_env_file"
+mv "$tmp_env_file" "$HEALTHCHECK_ENV_FILE"
+
+exec "$STATSD_EXPORTER_BIN" "$@"