IP Allocation

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When a pod is creating, it will follow steps below to get IP allocations.

1. Get all IPPool candidates.

   For which IPPool is used by a pod, the following rules are listed from high to low priority which means the previous rule would override the latter rule.

   • SpiderSubnet annotation. ipam.spidernet.io/subnets and ipam.spidernet.io/subnet will choose to use auto-created ippool if the SpiderSubnet feature is enabled. See SpiderSubnet for details.
   • Honor pod annotation. ipam.spidernet.io/ippools" and "ipam.spidernet.io/ippool could be used to specify an ippool. See Pod Annotation for details.
   • Namespace annotation. ipam.spidernet.io/defaultv4ippool and ipam.spidernet.io/defaultv6ippool could be used to specify an ippool. See namespace annotation for details.
   • CNI configuration file. It can be set to default_ipv4_ippool and default_ipv6_ippool in the CNI configuration file. See configuration for details.
   • Cluster default IPPool. We can set SpiderIPPool CR object with default property, in which we'll regard it as a default pool in cluster. See configuration for details.

2. Filter valid IPPool candidates.

   After getting IPv4 and IPv6 IPPool candidates, it looks into each IPPool and figures out whether it meets following rules, and learns which candidate IPPool is available.

   • Filter terminating IPPools.
   • The disable field of the IPPool is false. This property means the IPPool is not available to be used.
   • Check IPPool.Spec.NodeName and IPPool.Spec.NodeAffinity properties whether match the scheduled node of the pod or not. If not match, this IPPool would be filtered. (NodeName has higher priority than NodeAffinity)
   • Check IPPool.Spec.NamespaceName and IPPool.Spec.NamespaceAffinity properties whether match the namespace of the pod or not. If not match, this IPPool would be filtered. (NamespaceName has higher priority than NamespaceAffinity)
   • The IPPool.Spec.PodAffinity field of the IPPool must meet the pod
   • Check IPPool.Spec.MultusName properties whether match the pod current NIC Multus configuration or not. If not match, this IPPool would be filtered.
   • The available IP resource of the IPPool is not exhausted

3. Sort IPPool candidates.

We'll sort these IPPool candidates with our custom priority rules, then the IPAM prefers allocating IP addresses from the candidates in sequence.

• The IPPool resource with IPPool.Spec.PodAffinity property has the highest priority.
• The IPPool resource with IPPool.Spec.NodeName or IPPool.Spec.NodeAffinity property has the second-highest priority.
• The IPPool resource with IPPool.Spec.NamespaceName or IPPool.Spec.NamespaceAffinity property has the second-highest priority.
• The IPPool resource with IPPool.Spec.MultusName property has the lowest priority.

Notice: here are some simple instance to describe this rule.

1. IPPoolA with properties IPPool.Spec.PodAffinity and IPPool.Spec.NodeName has higher priority than IPPoolB with single affinity property IPPool.Spec.PodAffinity.
2. IPPoolA with single property IPPool.Spec.PodAffinity has higher priority than IPPoolB with properties IPPool.Spec.NodeName and IPPool.Spec.NamespaceName.
3. IPPoolA with properties IPPool.Spec.PodAffinity and IPPool.Spec.NodeName has higher priority than IPPoolB with properties IPPool.Spec.PodAffinity,IPPool.Spec.NamespaceName and IPPool.Spec.MultusName.

1. Assign IP from valid IPPool candidates.

   When trying to assign IP from the IPPool candidates, it follows rules as below.

   • The IP is not reserved by the "exclude_ips" field of the IPPool and all ReservedIP instances

Notice: If the pod belongs to StatefulSet, it would be assigned IP addresses with the upper rules firstly. And it will try to reuse the last allocated IP addresses once the pod 'restarts'.