ci: report candidate container failures

scripts/deploy.mjs

@@ -41,6 +41,21 @@ async function waitForHealth(container, timeoutMs = 90_000) {
   throw new Error("Timed out waiting for candidate health check");
 }
 
+async function reportContainerFailure(container) {
+  try {
+    const state = await container.inspect();
+    console.error(`Candidate status: ${state.State.Status}; health: ${state.State.Health?.Status || "unavailable"}`);
+    for (const check of state.State.Health?.Log?.slice(-3) || []) {
+      const output = check.Output?.trim();
+      if (output) console.error(`Health check: ${output}`);
+    }
+    const logs = await container.logs({ stdout: true, stderr: true, tail: 100 });
+    if (logs.length) console.error(`Candidate logs:\n${logs.toString("utf8")}`);
+  } catch (diagnosticError) {
+    console.error(`Could not read candidate diagnostics: ${diagnosticError.message}`);
+  }
+}
+
 async function followBuild(stream) {
   const output = await new Promise((resolve, reject) => {
     docker.modem.followProgress(stream, (error, events) => error ? reject(error) : resolve(events), (event) => {
@@ -93,7 +108,10 @@ try {
   if (hasCurrent) await removeContainer(previous);
   console.log(`Deployed ${image} on port ${port}`);
 } catch (error) {
-  if (next) await removeContainer(candidate).catch(() => undefined);
+  if (next) {
+    await reportContainerFailure(next);
+    await removeContainer(candidate).catch(() => undefined);
+  }
   if (hasCurrent) {
     const rollback = docker.getContainer(previous);
     await rollback.rename({ name: service });