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Probe type · Pro+

WebSocket probe

The only check that proves your WebSocket endpoint actually upgrades, negotiates the right subprotocol, and stays responsive after the 101.

Why you need it

A WebSocket probe exercises every phase of a real WebSocket connection — DNS, TCP, TLS, HTTP Upgrade, subprotocol negotiation, and an actual send / receive round-trip after the 101. An HTTP probe stops at the response status code; a TCP probe never even tries the Upgrade. Neither catches the failure modes that hit WebSocket apps in production.

Three depth levels:

  • Level 1 — Connect + 101. DNS → TCP → TLS → GET with Upgrade: websocket + Sec-WebSocket-Key → server returns 101 Switching Protocols.
  • Level 2 — Subprotocol assertion. Offer subprotocols (e.g. graphql-ws, graphql-transport-ws) and assert that the server's Sec-WebSocket-Protocol response matches. Catches silent server changes that upgrade fine but no longer support your client's protocol.
  • Level 3 — Send/receive RTT. After the 101 the probe sends a small text frame (default "ping") and waits for a response. Echo semantics by default; switchable to "any non-control frame counts" for servers that emit a welcome frame.

The Upgrade handshake runs over HTTP/1.1 by default. For environments that already run WebSockets over HTTP/2 via RFC 8441's CONNECT extension, an HTTP/2 mode is one toggle away. A single auth-style header is AES-GCM encrypted at rest; additional non-secret headers live in a separate JSON field.

Where it pays off

Use a WebSocket probe whenever your product's real-time path matters and HTTP polling can't tell you it's healthy:

  • GraphQL subscriptions — assert the graphql-transport-ws subprotocol negotiates and a ping frame round-trips inside the budget.
  • Chat / collaboration apps — Slack-style real-time infra where the WebSocket is the product. Level 3 RTT catches the wedged-event-loop failure.
  • Phoenix / Rails ActionCable / SignalR — frameworks that emit a welcome frame on connect. Set "Expect echo" to off.
  • MQTT-over-WebSocket and trading APIs — financial and IoT exchanges publishing prices over WSS.
  • Authenticated WebSocket APIs — Bearer token or API-key in the encrypted Auth field.

Not the right choice when: the endpoint speaks long-poll HTTP rather than WebSockets — use the HTTP probe. Also a poor fit for Server-Sent Events (SSE) — that's an HTTP/2 stream and reachable from the HTTP probe.

Configuration parameters

Field Type Required Default Description
Name string Required — Human-readable label for the probe.
Target URL string (ws:// or wss://) Required — Full WebSocket URL. wss:// preferred for production. Internal hostnames rejected at save time.
HTTP version Http11 | Http2 Optional Http11 Transport version. HTTP/2 (RFC 8441) requires server SETTINGS_ENABLE_CONNECT_PROTOCOL; falls back to HTTP/1.1.
Offered subprotocols string (comma-separated) Optional — Subprotocols the client offers (e.g. "graphql-ws, graphql-transport-ws").
Expected subprotocol string Optional — Hard assertion — server's chosen subprotocol must equal this value or the probe flips Down.
Origin header string Optional — Value of the Origin request header. Required by CSRF-aware servers.
Custom headers JSON object Optional — Map of header → value sent on the Upgrade request. Non-secret only — use Auth header for credentials.
Auth header string (encrypted at rest) Optional — Single auth-style line (Bearer / X-API-Key). AES-GCM encrypted; sent as Authorization.
Send RTT probe boolean Optional true When on, after the 101 the probe sends a small text frame and waits for a response (Level 3).
RTT payload string Optional ping Text payload for the RTT probe. Capped at 64 KB.
Expect echo boolean Optional true When on, server response must equal what we sent. When off, any non-control frame counts (welcome frame servers).
Handshake Degraded (ms) integer Optional 1000 Connect + TLS + Upgrade budget above which the probe reports Degraded.
RTT Degraded (ms) integer Optional 200 Post-101 send/receive latency above which the probe reports Degraded.
RTT timeout (ms) integer Optional 5000 Hard ceiling on the RTT-probe response.
Ignore server cert validation boolean Optional false Accept self-signed or untrusted server certs.

Available on Pro+. Already on StatusPulse? See the full config in Help →

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