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Pools

A pool is a group of origin servers, with each origin identified by its IP address or hostname.

If you are familiar with DNS terminology, think of a pool as a “record set,” except Cloudflare only returns addresses that are considered healthy. You can attach health checks to individual pools for customized monitoring.


Important notes

When working with pools, note the following:

When adding origin servers to a pool, you can identify the origin by hostname or IP address.

The order of pools in the load balancer determines the standard failover priority. When the number of healthy origins in a pool drops below the configured threshold, Load Balancing routes traffic to the next available pool.

By default, pools are ordered by date created. You can reorder them from the Load Balancing dashboard and via Cloudflare API (use the Update Pools command to set a new origins array).

Dynamic Steering uses Round Trip Time (RTT) profiles to determine pool priority. If there is no RTT data for a pool in a region or colocation center, Load Balancing will use pool order to determine failover priority.

Geo Steering directs traffic to pools based on the client’s region or point of presence. If there is no Geo Steering configuration for a region or pool, the load balancer will use pool order to determine failover priority.


Properties

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


Per origin Host header override

To balance traffic across multiple hosts, add Host headers to individual origins within the same pool.

For example, you might have a pool with origins hosted in multiple AppEngine projects or Amazon S3 buckets. You also might want to set up specific failover origins within a pool.

Since these examples require specific hostnames per origin, your load balancer could not properly route traffic without a Host header override.

If you need an origin Host header override, add it when creating or editing a pool. For security reasons, this header must meet one of the following criteria:

  • Is a subdomain of a zone associated with this account
  • Matches the origin address
  • Publicly resolves to the origin address

For details about how origin and monitor Host headers interact, see Host header prioritization.


Create pools

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


API commands

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

CommandMethodEndpoint
Create PoolPOSTuser/load_balancers/pools
Delete PoolDELETEuser/load_balancers/pools/:identifier
List PoolsGETuser/load_balancers/pools
Pool DetailsGETuser/load_balancers/pools/:identifier
Pool Health DetailsGETuser/load_balancers/pools/:identifier/health
Update PoolPUTuser/load_balancers/pools/:identifier
Preview PoolPOSTuser/load_balancers/pools/:identifier/preview
List Pool ReferencesGETuser/load_balancers/pools/:identifier/references