From c871ec2a1fca7deed89d2680221b3a1b913431be Mon Sep 17 00:00:00 2001
From: Samuel Scard <10246309+SamJamS@users.noreply.github.com>
Date: Sat, 20 Apr 2024 00:36:19 +0100
Subject: [PATCH 1/2] sidecar: set to not ready when failing to fetch
 prometheus version

Signed-off-by: Samuel Scard <10246309+SamJamS@users.noreply.github.com>
---
 cmd/thanos/sidecar.go | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cmd/thanos/sidecar.go b/cmd/thanos/sidecar.go
index 74ab3090fa..79535ee25c 100644
--- a/cmd/thanos/sidecar.go
+++ b/cmd/thanos/sidecar.go
@@ -189,6 +189,8 @@ func runSidecar(
 						"msg", "failed to fetch prometheus version. Is Prometheus running? Retrying",
 						"err", err,
 					)
+					promUp.Set(0)
+					statusProber.NotReady(err)
 					return err
 				}
 

From 12c399c250f27ebc6e94a2e70f07dd3a8a7c926c Mon Sep 17 00:00:00 2001
From: Samuel Scard <10246309+SamJamS@users.noreply.github.com>
Date: Sat, 20 Apr 2024 00:37:08 +0100
Subject: [PATCH 2/2] add TestSidecarNotReadyNoPrometheus

Signed-off-by: Samuel Scard <10246309+SamJamS@users.noreply.github.com>
---
 test/e2e/query_test.go | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/test/e2e/query_test.go b/test/e2e/query_test.go
index 78b92c3eac..e555bebd73 100644
--- a/test/e2e/query_test.go
+++ b/test/e2e/query_test.go
@@ -235,6 +235,39 @@ func TestSidecarNotReady(t *testing.T) {
 	}))
 }
 
+func TestSidecarNotReadyNoPrometheus(t *testing.T) {
+	t.Parallel()
+
+	e, err := e2e.NewDockerEnvironment("sidecar-noProm")
+	testutil.Ok(t, err)
+	t.Cleanup(e2ethanos.CleanScenario(t, e))
+
+	// Start sidecar without ever starting Prometheus.
+	_, sidecar := e2ethanos.NewPrometheusWithSidecar(e, "alone", e2ethanos.DefaultPromConfig("prom-alone", 0, "", "", e2ethanos.LocalPrometheusTarget), "", e2ethanos.DefaultPrometheusImage(), "")
+	testutil.Ok(t, sidecar.Start())
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	// Sidecar should not be ready if there was never a ready Prometheus.
+	testutil.Ok(t, runutil.Retry(1*time.Second, ctx.Done(), func() (rerr error) {
+		req, err := http.NewRequestWithContext(ctx, "GET", "http://"+sidecar.Endpoint("http")+"/-/ready", nil)
+		if err != nil {
+			return err
+		}
+		resp, err := http.DefaultClient.Do(req)
+		if err != nil {
+			return err
+		}
+		defer runutil.CloseWithErrCapture(&rerr, resp.Body, "closing resp body")
+
+		if resp.StatusCode == 200 {
+			return fmt.Errorf("got status code %d", resp.StatusCode)
+		}
+		return nil
+	}))
+}
+
 func TestQuery(t *testing.T) {
 	t.Parallel()