概要
服务部署在多个k8s集群中，往往希望服务跨多个集群进行调度设置。在federation v2中，可以通过ReplicaSchedulingPreference来满足联邦集群的调度设置。下面通过一个简单例子来介绍federation v2中ReplicaSchedulingPreference的用法。
原理分析
federation-controller-manager监听到ReplicaSchedulingPreference变化的时候，通过分析调度配置，生成FederatedDeployment（并且会监听该变化，进行终态保持，即要修改各个集群Deployment只能修改ReplicaSchedulingPreference），然后FederatedDeployment监听到变化会生成各个集群的Deployment。
环境准备
参考阿里云Kubernetes容器服务上体验Federation v2，完成两个集群的join，并配置好kubeconfig, 如下：
kubectl config get-contexts
CURRENT NAME CLUSTER AUTHINFO NAMESPACE
* cluster1 cluster1 kubernetes-admin1
cluster2 cluster2 kubernetes-admin2部署FederatedDeployment
执行如下yaml:
apiVersion: v1
kind: Namespace
metadata:
name: test-namespace
---
apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedNamespace
metadata:
name: test-namespace
namespace: test-namespace
spec:
placement:
clusterNames:
- cluster1
- cluster2
---
apiVersion: types.federation.k8s.io/v1alpha1
kind: FederatedDeployment
metadata:
name: test-deployment
namespace: test-namespace
spec:
template:
metadata:
labels:
app: nginx
spec:
replicas: 2
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- image: nginx
name: nginx
resources:
limits:
cpu: 500m
requests:
cpu: 200m
placement:
clusterNames:
- cluster1
- cluster2各个集群Deployment情况如下：
kubectl get deployment test-deployment -n test-namespace --context cluster1
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
test-deployment 2 2 2 2 8h
kubectl get deployment test-deployment -n test-namespace --context cluster2
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
test-deployment 2 2 2 2 8h配置ReplicaSchedulingPreference
apiVersion: scheduling.federation.k8s.io/v1alpha1
kind: ReplicaSchedulingPreference
metadata:
name: test-deployment
namespace: test-namespace
spec:
targetKind: FederatedDeployment
totalReplicas: 5
clusters:
"cluster1":
weight: 1
minReplicas: 1
"cluster2":
weight: 1
minReplicas: 1查看FederatedDeployment详情：
Name: test-deployment
Namespace: test-namespace
Labels: <none>
Annotations: <none>
API Version: types.federation.k8s.io/v1alpha1
Kind: FederatedDeployment
Metadata:
Creation Timestamp: 2019-05-16T02:39:09Z
Finalizers:
federation.k8s.io/sync-controller
Generation: 1
Resource Version: 218975248
Self Link: /apis/types.federation.k8s.io/v1alpha1/namespaces/test-namespace/federateddeployments/test-deployment
UID: c82681b0-7783-11e9-bcd8-e6193977a31d
Spec:
Overrides:
Cluster Name: cluster2
Cluster Overrides:
Path: spec.replicas
Value: 3
Cluster Name: cluster1
Cluster Overrides:
Path: spec.replicas
Value: 4
Placement:
Cluster Names:
cluster2
cluster1
Template:
Metadata:
Labels:
App: nginx
Spec:
Replicas: 2
Selector:
Match Labels:
App: nginx
Template:
Metadata:
Labels:
App: nginx
Spec:
Containers:
Image: nginx
Name: nginx可以看到FederatedDeployment信息已经被修改，查看各个集群Deployment详情：
kubectl get deployment test-deployment -n test-namespace --context cluster1
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
test-deployment 4 4 4 4 9h
kubectl get deployment test-deployment -n test-namespace --context cluster2
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
test-deployment 3 3 3 3 9h可以看到通过配置ReplicaSchedulingPreference来配置集群调度策略，当然还有其他的一些属性可以配置，比如每个集群的调度权重、最小副本数和最大副本数。
总结
在Federation v2联邦集群中，可以通过ReplicaSchedulingPreference来配置各个集群的调度策略，统一管理各个集群服务的分布。
