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In edge scenario, edge node can be offline since the network between edge and cloud is unstable, | ||
thanks to node autonomy feature provided by yurt-hub, pods can still be working, | ||
however there are some cases we need to take care. | ||
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### Flannel: keep Vtep mac address | ||
**Background** | ||
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If we use flannel as CNI plugin, in VXLAN mode, a Vtep device (usually named as "flannel.1") is created on each host, | ||
and the VNI, VtepMAC info are recorded in kube node annotation, consumed by other nodes to be aware and apply | ||
the corresponding routes and forwarding rules. | ||
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<div align="center"> | ||
<img src="../img/flannel-architecture.png" width=75% title="flannel-architecture" alt="flannel-architecture"> | ||
</div> | ||
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The flannel architecture is show in above pic, we take the two nodes as example. | ||
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Node2 created flannel.1 device with mac address "9e:c9:07:f9:b3:8b" and ip address "10.0.0.20", and update it in annotation. | ||
```yaml | ||
# node2 annotation with vtep info. | ||
flannel.alpha.coreos.com/backend-data: '{"VtepMAC":"9e:c9:07:f9:b3:8b"}' | ||
flannel.alpha.coreos.com/public-ip: 10.0.0.20 | ||
``` | ||
node1 will then set the fdb, arp, route entry in its host network namespace to form a L2 overlay tunnel. | ||
```shell script | ||
fdb: 9e:c9:07:f9:b3:8b dev flannel.1 dst 10.0.0.20 self permanent | ||
arp: ? (172.30.133.0) at 9e:c9:07:f9:b3:8b [ether] PERM on flannel.1 | ||
route: 172.30.133.0/26 via 172.30.133.0 dev flannel.1 onlink | ||
``` | ||
Each time node2 restarted, flannel will create new Vtep device with new mac address, and update the info in node2's annotation. | ||
However, if node2 is offline, the update cannot be truly done. Node1 will not be aware of the mac address change, | ||
this will cause pod connectivity issues between edge nodes. | ||
**Solution: Keep Vtep mac address in flannel** | ||
For each time flannel restarted and try to create new Vtep device, it reads the mac address from node annotation, | ||
either from kube-apiserver or yurt-hub local cache, and use it for Vtep device if exists. | ||
For this solution, there is minor code change in flannel. | ||
### IPAM: keep pod ip address | ||
**Background** | ||
In most cases, host-local IPAM is used for CNI plugin. It works by assigning free ip address for each new pod from node's CIDR range, | ||
and recording the assigned ips in local data directory, to denote them occupied. | ||
For example, if IPAM dataDir is configured as "/var/lib/cni/networks/cbr0", it looks like below, | ||
```shell script | ||
$ ls /var/lib/cni/networks/cbr0 | ||
172.30.132.194 172.30.132.198 172.30.132.201 | ||
``` | ||
For some edge application, static pod ip is required, which means pod ip address cannot be changed when it's recreated. | ||
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**Solution: Keep ip address in IPAM** | ||
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To support this, we need to adjust the IPAM plugin to record {ip}-{pod namespace}-{pod name} binding info, instead of single ips. | ||
For incoming ip allocation request, IPAM plugin will use the binded ip if same pod name already exists in data directory. | ||
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The record for each pod can be like: | ||
```shell script | ||
$ ls /var/lib/cni/networks/cbr0 | ||
172.30.132.194_kube-system_coredns-vstxh 172.30.132.198_kube-system_nginx-76df748b9-4cz95 172.30.132.201_kube-system_nginx-76df748b9-nf5l9 | ||
``` | ||
For this solution, there is minor code change in host-local IPAM plugin. |