Setting Up Primary-Secondary Stream Replication Manually

Describes how to setup a primary-secondary stream replica that replicates in one direction.

About this task

Replica streams can be in a remote data-fabric cluster or in the data-fabric cluster where their source streams are located. All updates from a source stream arrive at a replica stream after having been authenticated at a gateway. Therefore, the produceperm access control expressions on the replica stream is irrelevant; gateways have the implicit authority to publish messages to topics in replica streams.

To set up primary-secondary replication of streams:

Procedure

Create the replica manually with the maprcli stream create command. Use the -copymetafrom option to ensure that the metadata for the replica is identical to the metadata for the source stream.
```
maprcli stream create -path <path to replica> 
-copymetafrom <path to source stream>
```
For example, to create the replica activity in the newyork cluster and use the metadata from the source stream in the sanfrancisco cluster, you could use this command:
```
maprcli stream create -path /mapr/newyork/activity 
-copymetafrom /mapr/sanfrancisco/activity
```
Register the replica as a replica of the source stream by running the maprcli stream replica add command.
```
maprcli stream replica add -path <path to source stream> 
-replica <path to replica> -paused true
```
For example, to register the activity stream in the newyork cluster as a replica of the activity stream in the sanfrancisco cluster, you could use this command:
```
maprcli stream replica add -path /mapr/sanfrancisco/activity 
-replica /mapr/newyork/activity -paused true
```
The -paused parameter ensures that replication does not start immediately after you register the source stream as a source for this replica. You do this registration in step 4.
Verify that you specified the correct replica by running the maprcli stream replica list command.
```
maprcli stream replica list -path <path to source stream>
```
To verify that the activity stream in the newyork cluster is a replica of the activity stream in the sanfrancisco cluster, you could look at the output of this command:
```
maprcli stream replica list -path /mapr/sanfrancisco/activity
```
Authorize replication between the streams by defining the source stream as the upstream stream for the replica by running the maprcli stream upstream add command.
Definition of the upstream stream ensures that a stream cannot replicate updates to any replica. Replication depends on a two-way agreement between the owners of the two streams.
```
maprcli stream upstream add -path <path to replica> -upstream 
<path to source stream>
```
To add the activity stream in the sanfrancisco cluster as an upstream source for the activity stream in the newyork cluster:
```
maprcli stream upstream add -path /mapr/newyork/activity -upstream 
/mapr/sanfrancisco/activity
```
Verify that you specified the correct source stream by running the maprcli stream upstream list command.
```
maprcli stream upstream list -path <path to the replica>
```
To verify this in our example scenario, you could use this command:
```
maprcli stream upstream list -path /mapr/newyork/activity
```
Load the replica with data from the source stream by using the mapr copystream utility.

Start replication with the command

maprcli stream replica
                        resume

maprcli stream replica resume -path <path to the source stream> 
-replica <path to the replica>

For our example scenario, you could use this command:

maprcli stream replica resume -path mapr/sanfrancisco/activity 
-replica /mapr/newyork/activity