Health monitoring

Overview#

REST APIs will often be situated behind a load balancer that uses a monitor URL for its configuration. Having a load balancer query the QuestDB REST endpoints (on port 9000 by default) will cause internal logs to become excessively noisy. Additionally, configuring per-URL logging would increase server latency.

To provide a dedicated health check feature that would have no performance knock on other system components, we opted to decouple health checks from the REST endpoints used for querying and ingesting data. For this purpose, a min HTTP server runs embedded in a QuestDB instance and has a separate log and thread pool configuration.

Usage#

The min server is enabled by default and will reply to any HTTP GET request to port 9003:

GET health status of local instance
curl -v http://127.0.0.1:9003

The server will respond with a HTTP status code of 200, indicating that the system is operational:

200 'OK' response
* Trying 127.0.0.1...
* TCP_NODELAY set
* Connected to 127.0.0.1 (127.0.0.1) port 9003 (#0)
> GET / HTTP/1.1
> Host: 127.0.0.1:9003
> User-Agent: curl/7.64.1
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: questDB/1.0
< Date: Tue, 26 Jan 2021 12:31:03 GMT
< Transfer-Encoding: chunked
< Content-Type: text/plain
<
* Connection #0 to host 127.0.0.1 left intact

Path segments are ignored which means that optional paths may be used in the URL and the server will respond with identical results, e.g.:

GET health status with arbitraty path
curl -v http://127.0.0.1:9003/status

Configuration#

The configuration section for the min HTTP server is available in the minimal HTTP server reference.