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Configure Cluster Topology for MongoDB Resources

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  • Prerequisites
  • Procedure

You can configure the deployment topology of your MongoDB resources within Kubernetes by defining NodeAffinity and PodAffinity. NodeAffinity and PodAffinity specify where Kubernetes deploys MongoDB custom resources in your Kubernetes cluster.

You can implement node affinity by applying node labels to specific nodes within your Kubernetes cluster and defining labelSelector fields with corrosponding labels in your MongoDB CustomResourceDefinition. When you apply node labels and matching labelSelector values, Kubernetes only deploys a given MongoDB CustomResourceDefinition on the nodes you specify within your Kubernetes cluster. Implementing node affinity rules can be useful when deploying MongoDB resources in heterogeneous node groups, as it allows you to deploy specific resources on specific node varieties.

Similarly, you can implement Pod affinity by applying labels to Pods that are running in your cluster and aligning those label values with labelSelector values defined in your MongoDB CustomResourceDefinition. When you apply labels and matching labelSelector values, Kubernetes colocates MongoDB custom resource-managed Pods with Pods with matching labels applied. By collocating Pods, you can improve system performance and reduce latency between Pods that communicate regularly. You can also define Pod antiaffinity rules which allow you to specify Pods which should not be colocated.

For Standalone and Replica Set deployments, you can apply these affinity rules to the spec.podSpec of your MongoDB CustomResourceDefinition. For Sharded Cluster deployments, you can apply these affinity rules to the spec.configSrvPodSpec, spec.shardPodSpec, and spec.mongosPodSpec sections of your MongoDB CustomResourceDefinition.

You must deploy MonogDB resources, such as mongos, shards, and config servers in the case of a Sharded Cluster deployment, in the same namespace as the MongoDB resource. However, within that namespace, you can configure the nodeAffinity and podAffinity for mongos, shards, and config server resource types in the ShardedCluster CustomResourceDefinition.

Prerequisites

To configure the deployment topology for your MongoDB deployment, you must either have a MongoDB replica set deployed through the MongoDB Kubernetes Operator along with labels applied to the Kubernetes resources that will align with labelSelectors defined in the MongoDB CustomResourceDefinition or meet the following prerequisites:

Procedure

1

Update your MongoDB CRD manifest.

Populate the podTemplate.affinity sections of your MongoDB Sharded Cluster definition as shown in the following example:

1---
2apiVersion: mongodb.com/v1
3kind: MongoDB
4metadata:
5  name: my-sharded-cluster
6spec:
7  shardCount: 2
8  mongodsPerShardCount: 3
9  mongosCount: 2
10  configServerCount: 3
11  version: 6.0.0
12  service: my-service
13
14  opsManager:
15    configMapRef:
16      name: my-project
17  credentials: my-credentials
18  type: ShardedCluster
19
20  persistent: true
21  configSrvPodSpec:
22    podTemplate:
23      spec:
24        affinity:
25          podAffinity:
26            requiredDuringSchedulingIgnoredDuringExecution:
27              - labelSelector:
28                  matchExpressions:
29                    - key: security
30                      operator: In
31                      values:
32                        - S1
33                topologyKey: failure-domain.beta.kubernetes.io/zone
34          nodeAffinity:
35            requiredDuringSchedulingIgnoredDuringExecution:
36              nodeSelectorTerms:
37                - matchExpressions:
38                    - key: kubernetes.io/e2e-az-name
39                      operator: In
40                      values:
41                        - e2e-az1
42                        - e2e-az2
43          podAntiAffinity:
44            requiredDuringSchedulingIgnoredDuringExecution:
45            - podAffinityTerm:
46                topologyKey: nodeId
47  mongosPodSpec:
48    podTemplate:
49      spec:
50        affinity:
51          podAffinity:
52            requiredDuringSchedulingIgnoredDuringExecution:
53              - labelSelector:
54                  matchExpressions:
55                    - key: security
56                      operator: In
57                      values:
58                        - S1
59                topologyKey: failure-domain.beta.kubernetes.io/zone
60          nodeAffinity:
61            requiredDuringSchedulingIgnoredDuringExecution:
62              nodeSelectorTerms:
63                - matchExpressions:
64                    - key: kubernetes.io/e2e-az-name
65                      operator: In
66                      values:
67                        - e2e-az1
68                        - e2e-az2
69          podAntiAffinity:
70            requiredDuringSchedulingIgnoredDuringExecution:
71            - podAffinityTerm:
72                topologyKey: nodeId
73  shardPodSpec:
74    podTemplate:
75      spec:
76        affinity:
77          podAffinity:
78            requiredDuringSchedulingIgnoredDuringExecution:
79              - labelSelector:
80                  matchExpressions:
81                    - key: security
82                      operator: In
83                      values:
84                        - S1
85                topologyKey: failure-domain.beta.kubernetes.io/zone
86          nodeAffinity:
87            requiredDuringSchedulingIgnoredDuringExecution:
88              nodeSelectorTerms:
89                - matchExpressions:
90                    - key: kubernetes.io/e2e-az-name
91                      operator: In
92                      values:
93                        - e2e-az1
94                        - e2e-az2
95          podAntiAffinity:
96            requiredDuringSchedulingIgnoredDuringExecution:
97            - podAffinityTerm:
98                topologyKey: nodeId
99...
2

Apply your changes.

kubectl apply -f mongodb-crd.yaml

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