The ironic.common.hash_ring Module

class ironic.common.hash_ring.HashRing(hosts, replicas=None)

Bases: object

A stable hash ring.

We map item N to a host Y based on the closest lower hash:

• hash(item) -> partition
• hash(host) -> divider
• closest lower divider is the host to use
• we hash each host many times to spread load more finely as otherwise adding a host gets (on average) 50% of the load of just one other host assigned to it.

get_hosts(data, ignore_hosts=None)

Get the list of hosts which the supplied data maps onto.

Parameters:

• data – A string identifier to be mapped across the ring.
• ignore_hosts – A list of hosts to skip when performing the hash. Useful to temporarily skip down hosts without performing a full rebalance. Default: None.

Returns:

a list of hosts. The length of this list depends on the number of replicas this HashRing was created with. It may be less than this if ignore_hosts is not None.

class ironic.common.hash_ring.HashRingManager

Bases: object

classmethod reset()