Remove init containers

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

packages/docker/prometheus/default.nix

@@ -1,21 +1,34 @@
 { pkgs, ... }:
+let
+  entrypoint = pkgs.writeTextFile {
+    name = "entrypoint";
+    executable = true;
+    destination = "/bin/entrypoint";
+    text = builtins.readFile ./entrypoint.sh;
+  };
+in
 pkgs.dockerTools.buildImage {
   name = "prometheus";
   fromImage = import ../base { inherit pkgs; };
 
   copyToRoot = pkgs.buildEnv {
     name = "root";
-    paths = with pkgs; [ prometheus ];
+    paths = with pkgs; [
+      entrypoint
+      prometheus
+      yq-go
+    ];
     pathsToLink = [ "/bin" ];
   };
 
   config = {
-    Entrypoint = [ "prometheus" ];
+    Entrypoint = [ "entrypoint" ];
     ExposedPorts = {
       "9090/tcp" = { };
     };
     WorkingDir = "/var/lib/prometheus";
     Volumes = {
+      "/etc/prometheus" = { };
       "/var/lib/prometheus" = { };
     };
   };

packages/docker/prometheus/entrypoint.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env sh
+
+set -o errexit
+set -o nounset
+
+if [ -d /etc/prometheus/conf.d ]; then
+  # shellcheck disable=SC2016
+  yq eval-all '. as $item ireduce ({}; . *+ $item)' /etc/prometheus/conf.d/*.yaml > /etc/prometheus/prometheus.yaml
+fi
+
+exec prometheus \
+  --config.file=/etc/prometheus/prometheus.yaml \
+  --storage.tsdb.path=/var/lib/prometheus \
+  "$@"