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TCP check

A TCP check connects to an endpoint on a given hostname or IP address and a port. This ensures a server accepts the connection and measures response latency and uptime. TCP checks operate at the transport layer and are ideal for monitoring TCP-based services such as mail servers, FTP servers, and message queues.

Create a TCP check

You can create and execute a TCP check from the Synthetic Monitoring UI.

  1. On the left-side menu, select Testing & synthetics > Synthetics.
  2. Click Create new check or Add new check.
  3. Choose API Endpoint as your check type.
  4. Set the value for the required options.
  5. Schedule or run the check.
    1. Click Save to schedule the check.
    2. Click Test to run the TCP check.

Options

The list of common options to all check types:

OptionDescription
EnabledWhether the check is enabled or not.
Job nameRefer to the check name. Check metrics include a job label with the value of this option.
TargetTarget of the check request. Check metrics include an instance label with the value of this option.
Probe locationsThe locations where the check should run from. Check metrics include a probe label with the value of the probe location running the check.
FrequencyThe frequency the check should run in seconds. The value can range from 60 to 3600 seconds. Only the sm_check_info metric includes the frequency label.
TimeoutMaximum execution time for the check. The value can range from 1 to 60 seconds.
Custom labels(Optional) Custom labels applied to check metrics. Refer to Custom labels for querying instructions.

Additionally, TCP checks have the following options:

OptionDescription
Use TLSWhether or not TLS is used when the connection is initiated.
Query and responseThe response to expect and the data to send.
Disable target certificate validationWhether to validate the certificate that is presented.
Server nameThe server name used during certificate validation.
CA certificateThe certificate for the certificate authority.
Client certificateThe client certificate to present during authentication.
Client keyThe corresponding key for the client certificate.
IP versionThe internet protocol version to use (V4, V6, or any).
Publish full set of metricsWhether to publish additional metrics to create histograms (used for Apdex scores or heatmaps). Default is false to reduce the number of active series.

These last options don’t produce any additional labels in the resulting check metrics.

Metrics

Checks store their results as Prometheus metrics, including the list of common metrics:

MetricDescription
probe_all_duration_secondsReturns how long the probe took to complete in seconds (histogram).
probe_duration_secondsReturns how long the probe took to complete in seconds.
probe_all_successDisplays whether or not the probe was a success (summary).
probe_successDisplays whether or not the probe was a success.
sm_check_infoProvides information about a single check configuration.

Additionally, TCP checks produce the following metrics:

MetricDescription
probe_dns_lookup_time_secondsReturns the time taken for probe DNS lookup in seconds.
probe_failed_due_to_regexIndicates if probe failed due to regular expression.
probe_ip_addr_hashSpecifies the hash of the IP address. It’s useful to detect if the IP address changes.
probe_ip_protocolSpecifies whether the probe IP protocol is IP4 or IP6.
probe_ssl_earliest_cert_expiryReturns last SSL chain expiry in Unix time.
probe_ssl_last_chain_expiry_timestamp_secondsReturns last SSL chain expiry in timestamp.
probe_ssl_last_chain_infoContains SSL leaf certificate information.
probe_tls_version_infoReturns the TLS version used or NaN when unknown.