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Probe ports and HTTP endpoints

Configure Categraf TCP, UDP and HTTP probes, then verify result codes, response content and certificate expiry metrics.

Last reviewed

By the end of this page, an independent probe will check service ports and HTTP responses rather than process existence alone. The configuration targets Categraf v0.5.17 and Nightingale v9.

TCP and UDP​

Edit conf/input.net_response/net_response.toml:

[[instances]]
targets = ["127.0.0.1:22"]
protocol = "tcp"
timeout = "2s"
labels = { probe = "ssh-local" }

Replace the target. A successful TCP connection proves that the port accepts connections, not that the application is healthy. Configure a protocol-appropriate send and expect pair when response checking is required.

UDP needs a meaningful request and expected reply. Changing protocol to udp alone does not make a complete probe. See the net_response configuration.

HTTP​

Edit conf/input.http_response/http_response.toml:

[[instances]]
targets = ["http://127.0.0.1:8080/health"]
method = "GET"
response_timeout = "5s"
expect_response_status_code = 200
expect_response_substring = "ok"
follow_redirects = false
labels = { probe = "application-health" }

Use the application's actual health endpoint and response. Check both status and body. Enable redirect following deliberately so a login redirect does not masquerade as health. HTTPS targets can also produce certificate-expiry metrics.

Verify and alert​

./categraf --test --inputs net_response:http_response

Expected result: net_response_result_code or http_response_result_code for the intended target. Zero means the configured check succeeded; nonzero means failure. The plugins use different nonzero codes, so do not share their error-code descriptions.

Restart collection after testing and check labels, result codes and timestamps in the destination store. Start with a result_code != 0 condition, an appropriate sustained duration and a meaningful severity.

When an HTTPS target produces http_response_cert_expire_timestamp, this expression returns seconds until expiry:

http_response_cert_expire_timestamp - time()

Verify the metric exists before enabling an expiry threshold. DNS, network access and probe permissions also affect results; a failed probe does not necessarily mean a process exited.

Next​

Full HTTP options: v0.5.17 configuration.

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