## It's necessary to add a mechanism to support client switch connection
between different pulsar cluster.
### Motivation
Generally, we can use DNS or TCP proxy to improve broker availability when you
have many pulsar cluster and one cluster is not available(such as network
error). But in this solution, we need a backup cluster, the backup cluster has
the same configurations. And in this solution have a problem with only can
close connection by broker(shut down the broker or setting the network or
offload namespace) to trigger client reconnect. So i have a idea, we can
trigger client reconnect by pulsar client.
### Implement
By now, we can create a pulsar client use service url. We can add a method
named serviceUrlProvider to create a pulsar client.
```java
public interface ServiceUrlProvider {
/**
* Get pulsar service url from ServiceUrlProvider.
*
* @return pulsar service url.
*/
String getServiceUrl();
/**
* Set pulsar client to the provider for provider can control the pulsar
client,
* such as {@link PulsarClient#forceCloseConnection()} or {@link
PulsarClient#close()}.
*
* @param client created pulsar client.
*/
void setClient(PulsarClient client);
}
```
We can create custom provider by ServiceUrlProvider such as
ZookeeperServiceUrlProvider. ZookeeperServiceUrlProvider can watch zookeeper
node update event then trigger pulsar client to reconnect the new service url.
We can add method like this:
```java
public void onServiceUrlChanged(String newServiceUrl) throws
PulsarClientException {
this.getPulsarClient().getConf().setServiceUrl(newServiceUrl);
this.getPulsarClient().reloadLookUp();
this.getPulsarClient().forceCloseConnection();
}
```
In this solution we switch client connection simpler and no need to do any
thing in pulsar broker.
[ Full content available at:
https://github.com/apache/incubator-pulsar/issues/2551 ]
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