Liveness Test

You can use liveness tests to determine whether your servers are live or down. Liveness testing is optional and not available with all property types.

Auto-generated host headers

The HTTP protocol requires clients to send a Host header, which indicates the hostname of the server the client expects talk to. This same value is also used as the Server Name Indication (SNI) in the TLS handshake. Because the value is required, if you do not specify a Host header, one will be automatically generated from the name of the property. For example, if your GTM domain is, and your property is named “test”, any HTTP liveness tests for that property sends the Host header “”, unless you explicitly set a Host header.

Liveness test coalescing

When GTM determines that multiple liveness tests for a given IP are functionally identical, it coalesces them into a single liveness test. This coalescing occurs across properties, as long as both properties use the same server IPs. If the test in question does not specify a Host header, an auto-generated one is used as described above. This feature, combined with test coalescing, can result in a test that sends an unexpected Host header. For example, properties “alpha” and “beta” both have HTTPs liveness tests, and both use the same server: Neither liveness test specifies a Host header, so an auto-generated one is used. Because the tests are functionally identical, GTM will coalesce them by picking one to use. This can result in only ever receiving a Host header of “”, and never “”.

To avoid this problem, always specify a Host header in HTTP and HTTPS liveness tests.

Liveness Test
Field Function
Enabled Click the Enabled checkbox to allow (enable) the liveness test for the selected property. Uncheck the box to disable the liveness test for the selected property.
Test Name Specifies a name for the liveness test. This field is required.
Test Interval Specifies, in seconds, how often liveness tests are run. The default is 60 seconds.
Test Timeout Specifies, in seconds, how long the servermonitor waits without getting a response before declaring a timeout error. The default is 25 seconds. See Timeout back off for more information.
Port Specify the port number for requesting the test object or accept a protocol's default port. The default port varies depending on which protocol you select.
Note: You can override the default port but you will get a Nonstandard Port warning in yellow next to the port number.
Protocol Specifies the protocol used to monitor servers. You can select from the following protocols. The port defaults are in parentheses.
  • DNS (port 53)
  • DoH - DNS over HTTPS (port 443)
  • DoT - DNS over TLS (port 853)
  • FTP (port 21)
  • HTTP (the default; port 80)
  • HTTPS (port 443)
  • POP (port 110)
  • POPS (port 995)
  • SMTP (port 25)
  • SMTPS (port 465)
  • TCP (port default not specified)
  • TCPS (port default not specified)
HTTP Method Allows you to choose from among a list of HTTP methods in a drop-down menu. This drop-down menu appears only when you specify the HTTP or HTTPS protocol in the Protocols field.
  • GET
  • HEAD
  • POST
  • PUT



The default value for the HTTP Method is GET.

When you change the HTTP method to POST, PUT or PATCH, the HTTP Request Body field appears below the HTTP Headers section in the Liveness test page. See a description of HTTP Request Body field in the table below.

Test Object Path Specify a valid local path to the test object. Enter only the local part of the test object, for example, /storage/data/examples.html.
HTTP Headers
Note: You are strongly encouraged to set the “Host” header for HTTP and HTTPS liveness tests.
Select one or more HTTP headers from a standard list of HTTP header options. In the Name field pull-down menu, choose an HTTP header and specify its value. Click the green plus sign (+) next to a header row to see a new row from which you can choose additional HTTP headers.
Note: The HTTP headers option is available only when you select HTTP and HTTPs protocols.

Optionally, you can choose Other … , which allows you to specify one or more customized HTTP headers. The customized header name must contain only letters, digits, hyphens, underscores, and dots. Blank spaces causes an error when you try to submit and validate the changes. To return to the Name field pull-down menu, click the arrow located to the left of the header text field.

To verify the validity of the selected HTTP headers, click the Validate HTTP Headers button before you save the liveness test.

For detailed descriptions of standard HTTP headers, see

HTTP Request Body

Allows you to select two different views when you input or edit HTTP request body content: Text View and Base64 View.

Text View--allows you to specify plain text in the HTTP Request Body field. This content gets encoded into Base64 format when you submit the form.

Base64 View-- Displays the HTTP body content in Base64 format. The maximum length of the Base64 encoded string is 4,000.

You can toggle back and forth between these two views.

Note: Regardless of which view you choose to use to edit content, the value you specify in the Request Body field is either null (empty textbox or HTTP Request Body field is not applicable) or a string of base64-encoded text with no spaces.
HTTP/FTP Errors Specify the ranges of response codes to consider when using HTTP, HTTPS, or FTP test protocols.
Authentication Defines authentication of a liveness test. This is optional but if used both the username and password fields must be entered.
Save Liveness Test Click the Save Liveness Test button. The new liveness test name appears in the Liveness Test table. Click the Add to Change List button.
These protocols have fields not shown on the Liveness Test page.
DNS and TCP/TCPS protocol fields
Protocol Fields
  • Record Type: Click and select an option from: A, AAAA, AFSDB, CNAME, DNSKEY, DS, HINFO, LOC, MX, NAPTR, NS, NSEC3, NSEC3PARAM, PTR, RP, RRSIG, SOA, SPF, SRV, SSHFP, TXT, or Other Type
  • Numeric Type: This field appears only when you select the DNS protocol and select Other Type from the Record Type menu. The default is 0, which is not valid. You must change the 0 value to an integer value between 1 and 65535.
  • DNS Name: Enter a single, valid DNS name. This is required.
  • Answers Required: If you check this, the liveness test will fail if the server returns no answers. If you leave it unchecked, the liveness test will succeed if the server returns a response with a success (status) code, even if the response contains no answers. The default is false.
  • Recursion Requested: Click the checkbox if you want recursion. The default is false.
TCP/TCPS TCP and TCPS Test Strings: You can specify a request and response string to use in the liveness tests. When the servermonitor performs the test, it connects to the server at the port you specified. If no request or response string is supplied, the test succeeds at this point. If a request string is specified, servermonitor then sends the request string and waits for the server to send a response. If the response contains the response string in the first 8K characters of the response, then the liveness test succeeds, otherwise it fails.
Note: If you select one of the secure protocols for a liveness test (HTTPS, POPS, SMTPS, and TCPS), you can upload an SSL certificate for that test. See Upload an SSL certificate for a liveness test for more information.
Note: If you select the HTTPS protocol, the Certificate Verification checkbox appears below the Protocol field. Click the checkbox to verify the validity of an SSL certificate. This prevents sending traffic to an origin that is up but has an invalid or bad certificate, which can cause failure on the clients if they are sent to the origin.