docker: read the resolver file a container really uses (hq issue 348)

On 2026-10-09 the control node's route-proxy failed every lookup against 10.10.0.1 alone for twenty minutes while the machine's file listed both mesh resolvers; its copy lives under the runtime's root-only directory and no tool read it. docker_resolv_conf reads /etc/resolv.conf as the container sees it through the runtime's archive (docker cp, no exec), parses it, and says whether it lists the same resolvers as the machine.
2026-10-09 13:33:23 +02:00
parent c0fa282548
commit 2fde82993d
4 changed files with 213 additions and 0 deletions
@@ -70,6 +70,19 @@ func tools(c *Client) []stdio.Tool {
 				return c.Inspect(ctx, ref)
 			},
 		},
+		{
+			Name: "docker_resolv_conf",
+			Description: "The resolver file one container really uses (/etc/resolv.conf as it sees it, read through the runtime's archive, no exec): " +
+				"its nameservers, search and options and the raw text, beside the machine's own nameservers and whether they are the same.",
+			Input: map[string]any{"container": containerArg},
+			Run: func(args map[string]any) (any, error) {
+				ref, err := text(args, "container")
+				if err != nil {
+					return nil, err
+				}
+				return c.ResolvConfOf(ctx, ref)
+			},
+		},
 		{
 			Name: "docker_logs",
 			Description: "The last lines one container wrote, both streams merged in order, each with its timestamp (default 200, at most 2000 lines; a line is cut at 4 KiB). " +