Cross data center replication example of multiple clusters

Review the cross data center replication example to understand how you can configure and start replication with Streams Replication Manager in a deployment with three data centers that each have two Kafka clusters.

In more advanced deployments, you may have multiple Kafka clusters in each of several data centers. To prevent creating a fully-connected mesh of all Kafka clusters, Cloudera recommends leveraging a single Kafka cluster in each data center for cross data center replication.

This example demonstrates the steps required to configure the deployment shown below. Additionally, it provides example commands that start bidirectional replication of all topics within each data center as well as example commands that replicate a single topic across all data centers

Figure 1. Cross Data Center Replication of Multiple Clusters

The following list of steps assume that all clusters are unsecured.
The following list of steps assume that both Streams Replication Manager Service and Driver roles are running on all Kafka broker hosts. Additionally, both roles have a single target which is their co-located cluster (the cluster they are running in).
Clusters West 1, East 1, and South 1 are collectively referred to as primary clusters, while clusters West 2, East 2, and South 2 are collectively referred to as secondary clusters.
Steps 1 through 8 must be carried out on each of the clusters individually. That is, the properties presented in these steps must be configured on all clusters. However, how you configure the properties for each individual cluster (the values that you set) will be different. The steps provide an explanation for each configuration and provide explicit examples for the clusters in Data Center West.
The following list of steps assume that the DefaultReplicationPolicy is in use.

Define the external Kafka cluster:
External clusters are configured with Kafka credentials. On each primary cluster you need to create a total of three Kafka credentials. Two representing the other two primary clusters and another one representing the secondary cluster that is in the same data center. On each secondary cluster you need to create a single Kafka credential representing the primary cluster that is running in the same data center.
1. In Cloudera Manager, go to Administration > External Accounts.
2. Go to the Kafka Credentials tab.
3. Click Add Kafka credentials.
4. Configure the Kafka credentials.
  For example, in West 1, you need to create credentials for East 1, South 1, and West 2. In West 2, you need to create a credential for West 1.
  - West 1
    East 1 Credential
    South 1 Credential
    West 2 Credential
    Name=east1 Bootstrap servers=east1-host1.cloudera.com:9092, east1-host2.cloudera.com:9092, east1-host2.cloudera.com:9092 Security protocol=PLAINTEXT
    Name=south1 Bootstrap servers=south1-host1.cloudera.com:9092, south1-host2.cloudera.com:9092, south1-host2.cloudera.com:9092 Security protocol=PLAINTEXT
    Name=west2 Bootstrap servers=west2-host1.cloudera.com:9092, west2-host2.cloudera.com:9092, west2-host2.cloudera.com:9092 Security protocol=PLAINTEXT
  - West 2
    West 1 Credential
    Name=west1 Bootstrap servers=west1-host1.cloudera.com:9092, west1-host2.cloudera.com:9092, west1-host2.cloudera.com:9092 Security protocol=PLAINTEXT
5. Click Add.
  If credential creation is successful, a new entry corresponding to the Kafka credential you specified appears on the page.
Define the co-located Kafka cluster:
1. In Cloudera Manager, go to Clusters and select the Streams Replication Manager service.
2. Go to Configuration.
3. Find and enable the Kafka Service property.
4. Find and configure the Streams Replication Manager Co-located Kafka Cluster Alias property.
  The alias you configure represents the co-located cluster. Enter an alias that is unique and easily identifiable.
  For example:
  - West 1
    west1
  - West 2
    west2
Add the clusters defined with Kafka credentials to SRM’s configuration:
1. Find and configure the External Kafka Accounts property.
2. Click the add button and add new lines for each Kafka credential you created.
3. Add the names of all Kafka credentials.
  Add each Kafka credential that you created in the cluster that you are configuring. When configured correctly, the property will include three credential names in each primary and a single credential name in each secondary cluster. Each Kafka credential must be added to a new line.
  For example, in West 1 you must add the names of the Kafka credentials that you created in West 1:
```
east1
south1
west2
```
  In West 2, you must add a the name of the single credential created for West 1:
```
west1
```
Find and configure the Streams Replication Manager Cluster alias property.
Add all cluster aliases to this property. This includes the aliases present in both the External Kafka Accounts and Streams Replication Manager Co-located Kafka Cluster Alias properties. Delimit the aliases with commas. For example:
- West 1
```
west1, west2, east1, south1
```
- West 2
```
west1, west2
```
Add and enable replications:
1. Find the Streams Replication Manager's Replication Configs property.
2. Click the add button and add new lines for each unique replication you want to add and enable.
3. Add and enable your replications.
  In the case of this example, you need to enable both cross data center replication and replication within each data center. This can be done by configuring three replications in each primary cluster and a single replication in each of the secondary clusters. Each of the replications that you configure should target the cluster that you are configuring. For example:
  - West 1
    east1->west1.enabled=true south1->west1.enabled=true west2->west1.enabled=true
  - West 2
    west1->west2.enabled=true
Click Save Changes.
Restart the SRM service.
Start replication with the srm-control tool:
The following command examples demonstrate how you can start replication of a single topic across all data centers and how you can replicate all topics within each data center.
important
The following commands assume that the DefaultReplicationPolicy is in use. Running the following commands with the IdentityReplicationPolicy would result in replication loops.
1. SSH into one of the hosts in West 1 and run the following commands:
  Replicate topic1 across data centers.
```
srm-control topics --source east1 --target west1 --add topic1,east2.topic1
srm-control topics --source south1 --target west1 --add topic1,south2.topic1
```
  Replicate all topics within the data center.
```
srm-control topics --source west1 --target west2 --add ".*"
srm-control topics --source west2 --target west1 --add ".*"
```
2. SSH into one of the hosts in East 1 and run the following commands:
  Replicate topic1 across data centers.
```
srm-control topics --source west1 --target east1 --add topic1,west2.topic1
srm-control topics --source south1 --target east1 --add topic1,south2.topic1
```
  Replicate all topics within the data center.
```
srm-control topics --source east1 --target east2 --add ".*"
srm-control topics --source east2 --target east1 --add ".*"
```
3. SSH into one of the hosts in South 1 and run the following commands:
  Replicate topic1 across data centers.
```
srm-control topics --source west1 --target south1 --add topic1,west2.topic1
srm-control topics --source east1 --target south1 --add topic1,east2.topic1
```
  Replicate all topics within the data center.
```
srm-control topics --source south1 --target south2 --add ".*"
srm-control topics --source south2 --target south1 --add ".*"
```