Monitors

A monitor issues health monitor requests at regular intervals to evaluate the health of each endpoint within a pool.

When a pool becomes unhealthy, your load balancer takes that pool out of the endpoint rotation.

    flowchart RL
      accTitle: Load balancing monitor flow
      accDescr: Monitors issue health monitor requests, which validate the current status of servers within each pool.
      Monitor -- Health Monitor ----> Endpoint2
      Endpoint2 -- Response ----> Monitor
      subgraph Pool
      Endpoint1((Endpoint 1))
      Endpoint2((Endpoint 2))
      end

Health monitor requests that result in a status change for an endpoint are recorded as events in the Load Balancing event logs.

Note

Health monitors associated with load balancers are different from standalone Health Checks. For an overview of how the Cloudflare Load Balancing solution works, refer to Load Balancing components.

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Properties

For an up-to-date list of monitor properties, refer to Monitor properties in our API documentation.

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Create monitors

For step-by-step guidance, refer to Create monitors.

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Health monitor regions

When you attach a monitor to a pool, you can select multiple regions to increase reporting accuracy.

For each option selected in a pool’s Health Monitor Regions, Cloudflare sends health monitor requests from three separate data centers in that region.

If the majority of data centers for that region pass the health monitor requests, that region is considered healthy. If the majority of regions is healthy, then the endpoint itself will be considered healthy.

Configurations

All Data Centers (Enterprise only)

Health monitor probes are sent from every single data center in Cloudflare’s network to the endpoints within the associated pool. This allows probes to hit each endpoint during intervals set by the customer.

All Regions

Three health monitor probes per region are sent to each endpoint in the associated pool. There are a total of 13 regions, resulting in 39 probes.

Regional

Three health monitor probes are sent from each specified region within the pool configuration.

Caution

Because of how Cloudflare checks health from multiple regions, adding multiple regions — or choosing to check health from All Data Centers — can send a lot of traffic to your endpoint.

The same problem can occur when setting low values for a monitor’s Interval.

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Host header prioritization

The host headers used on health monitor requests can be configured either on the monitor itself or on the endpoints within a pool.

When a host header is specified both on the monitor and on the endpoint, the host header configured on the endpoint takes precedence over the host header configured on the monitor.

When no host header is specified, Cloudflare uses the Endpoint Address configured on the endpoints as the host header for the health monitor requests.

For more details, refer to Override HTTP Host headers.

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API commands

The Cloudflare API supports the following commands for monitors. Examples are given for user-level endpoint but apply to the account-level endpoint as well.

Command	Method	Endpoint
Create Monitor	POST	accounts/:account_id/load_balancers/monitors
Delete Monitor	DELETE	accounts/:account_id/load_balancers/monitors/:id
List Monitors	GET	accounts/:account_id/load_balancers/monitors
Monitor Details	GET	accounts/:account_id/load_balancers/monitors/:id
Overwrite specific properties	PATCH	accounts/:account_id/load_balancers/monitors/:id
Overwrite existing monitor	PUT	accounts/:account_id/load_balancers/monitors/:id
Preview Monitor	POST	accounts/:account_id/load_balancers/monitors/:id/preview

Supported protocols

Cloudflare Load Balancing supports public monitoring for HTTP, HTTPS, TCP, UDP, ICMP, ICMP ping, and SMTP.

Load Balancing also supports private monitoring for HTTP, HTTPS, and TCP.