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.

On the left-side menu, select Testing & synthetics > Synthetics.
Click Create new check or Add new check.
Choose API Endpoint as your check type.
Set the value for the required options.
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:

Option	Description
Enabled	Whether the check is enabled or not.
Job name	Refer to the check name. Check metrics include a `job` label with the value of this option.
Target	Target of the check request. Check metrics include an `instance` label with the value of this option.
Probe locations	The locations where the check should run from. Check metrics include a `probe` label with the value of the probe location running the check.
Frequency	The frequency the check should run in seconds. The value can range from 10 to 3600 seconds. Only the `sm_check_info` metric includes the `frequency` label.
Timeout	Maximum 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:

Option	Description
Use TLS	Whether or not TLS is used when the connection is initiated.
Query and response	The response to expect and the data to send.
Disable target certificate validation	Whether to validate the certificate that is presented.
Server name	The server name used during certificate validation.
CA certificate	The certificate for the certificate authority.
Client certificate	The client certificate to present during authentication.
Client key	The corresponding key for the client certificate.
IP version	The IP version to use: `V4` (IPv4 only), `V6` (IPv6 only), or `Any` (prefers IPv6, falls back to IPv4). With `Any`, if no IPv6 (AAAA) record exists, the check uses IPv4 (A) records. The check doesn’t retry with a different IP version if the initial connection fails.
Publish full set of metrics	Whether 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:

Metric	Description
`probe_all_duration_seconds`	Returns how long the probe took to complete in seconds (histogram).
`probe_duration_seconds`	Returns how long the probe took to complete in seconds.
`probe_all_success`	Displays whether or not the probe was a success (summary).
`probe_success`	Displays whether or not the probe was a success.
`sm_check_info`	Provides information about a single check configuration.

Additionally, TCP checks produce the following metrics:

Metric	Description
`probe_dns_lookup_time_seconds`	Returns the time taken for probe DNS lookup in seconds.
`probe_failed_due_to_regex`	Indicates if probe failed due to regular expression.
`probe_ip_addr_hash`	Specifies the hash of the IP address. It’s useful to detect if the IP address changes.
`probe_ip_protocol`	Specifies whether the probe IP protocol is IP4 or IP6.
`probe_ssl_earliest_cert_expiry`	Returns last SSL chain expiry in Unix time.
`probe_ssl_last_chain_expiry_timestamp_seconds`	Returns last SSL chain expiry in timestamp.
`probe_ssl_last_chain_info`	Contains SSL leaf certificate information.
`probe_tls_version_info`	Returns the TLS version used or `NaN` when unknown.