Latency is the wall-clock time measured from the moment immediately before we send the probe request to the moment when we receive the last byte of the response. If for any reason (including network failure) a valid HTTP response isn't received for a probe, the probe is counted as a failure. Health probe responses ResponsesĪ 200 OK status code indicates the backend is healthy. For new Front Door profiles, by default, the probe method is set as HEAD.įor lower load and cost on your backends, Front Door recommends using HEAD requests for health probes. HEAD: The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response.GET: The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI.Supported HTTP methods for health probesĪzure Front Door supports the following HTTP methods for sending the health probes: These probes are sent over the same TCP ports configured for routing client requests, and cannot be overridden. Supported protocolsĪzure Front Door supports sending probes over either HTTP or HTTPS protocols. There could be more than one POP in each edge location.Īzure Front Door HTTP/HTTPS probes are sent with User-Agent header set with value: Edge Health Probe. For a list of edge locations, see edge locations by region for Azure Front Door. The probing requests will be less if there is no traffic sent to all of the edge POPs. The probe volume on each of your origin is equal to the number of edge POPs times two requests per minute. If there is customer traffic to all the Azure Front Door edge POP, the health probe volume can be high depending on your health probes frequency.Īn example to roughly estimate the health probe volume per minute to your origin when using the default probe frequency of 30 seconds. If the Azure Front Door edge POP doesn’t receive real traffic from your end users, the frequency of the health probe from the edge POP is decreased from the configured frequency. The number of probes depends on your customer's traffic location and your health probe frequency. Since each Azure Front Door edge POP emits health probes to your origins, the health probe volume for your origins can be quite high. Azure Front Door then uses these responses from the probe to determine the "best" origin to route your client requests. To determine the health and proximity of each backend for a given Azure Front Door environment, each Front Door environment periodically sends a synthetic HTTP/HTTPS request to each of your configured origins. An Origin and a origin group in this article refers to the backend and backend pool of the Azure Front Door (classic) configuration.
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