observability: run as container root 0:0, not 1000:1000

Measured the rootless mapping: container root IS the invoking user
(dank, owner of the /opt data dirs); the images' default users (loki
10001, prometheus nobody, grafana 472) map to subuids that own nothing.
1000:1000 was the wrong direction.

dankclaw/compose.yaml

@@ -103,9 +103,10 @@ services:
     image: docker.io/prom/prometheus:latest
     container_name: prometheus
     restart: unless-stopped
-    # Rootless: container uid 1000 maps to the invoking user, so the
+    # Rootless: container root maps to the invoking user (dank), which
-    # container can write its /opt/prometheus/data bind mount.
+    # owns /opt/prometheus/data. The image's default user (nobody) maps to
-    user: "1000:1000"
+    # a subuid that cannot write it.
+    user: "0:0"
     command:
       - --config.file=/etc/prometheus/prometheus.yml
       - --storage.tsdb.path=/prometheus
@@ -126,9 +127,10 @@ services:
     image: docker.io/grafana/grafana:latest
     container_name: grafana
     restart: unless-stopped
-    # Rootless: container uid 1000 maps to the invoking user, so the
+    # Rootless: container root maps to the invoking user (dank), which
-    # container can write its /opt/grafana/data bind mount.
+    # owns /opt/grafana/data. The image's default user (472) maps to a
-    user: "1000:1000"
+    # subuid that cannot write it.
+    user: "0:0"
     environment:
       GF_SERVER_ROOT_URL: "https://grafana.franksdank.cloud"
       GF_SECURITY_ADMIN_USER: "${GRAFANA_ADMIN_USER}"
@@ -150,9 +152,10 @@ services:
     image: docker.io/grafana/loki:latest
     container_name: loki
     restart: unless-stopped
-    # Rootless: container uid 1000 maps to the invoking user, so the
+    # Rootless: container root maps to the invoking user (dank), which
-    # container can write its /opt/loki/data bind mount.
+    # owns /opt/loki/data. The image's default user (10001) maps to a
-    user: "1000:1000"
+    # subuid that cannot write it.
+    user: "0:0"
     command: ["-config.file=/etc/loki/loki-config.yaml"]
     ports:
       - "3100:3100"

tests/caddyfile.bats

@@ -119,10 +119,11 @@ CADDYFILE="$REPO_ROOT/dankclaw/Caddyfile"
     ! grep -nE '^\s*-\s*"?http' "$REPO_ROOT/shared/prometheus/prometheus.yml"
 }
 
-@test "observability containers run as the host user (rootless uid mapping)" {
+@test "observability containers run as container root (rootless = host user)" {
-    # Rootless podman maps container uid 1000 to the invoking user, so
+    # In rootless podman, container root maps to the invoking user (dank),
-    # 1000:1000 lets these containers write their /opt data dirs. Container
+    # which owns the /opt data dirs. The images' default users (loki 10001,
-    # root would map to a subuid that owns nothing under /opt.
+    # prometheus nobody, grafana 472) map to subuids that own nothing under
+    # /opt and cannot write the data dirs.
     local compose="$REPO_ROOT/dankclaw/compose.yaml"
     local svc block
     for svc in prometheus loki grafana; do
@@ -130,8 +131,8 @@ CADDYFILE="$REPO_ROOT/dankclaw/Caddyfile"
             $0 ~ s { inblk = 1; next }
             inblk && /^  [a-z]/ { inblk = 0 }
             inblk' "$compose")
-        echo "$block" | grep -q 'user: "1000:1000"' || {
+        echo "$block" | grep -q 'user: "0:0"' || {
-            echo "service $svc does not run as user 1000:1000"; return 1;
+            echo "service $svc does not run as user 0:0"; return 1;
         }
     done
 }