2020-02-04 23:02:32 -05:00
|
|
|
# Restart Sequence
|
|
|
|
|
|
|
|
|
|
Apache ActiveMQ Artemis ships with 2 architectures for providing HA features.
|
|
|
|
|
The master and slave brokers can be configured either using network replication
|
|
|
|
|
or using shared storage. This document will share restart sequences for the
|
|
|
|
|
brokers under various circumstances when the client applications are
|
|
|
|
|
connected to it.
|
|
|
|
|
|
|
|
|
|
## Restarting 1 broker at a time
|
|
|
|
|
When restarting the brokers one at a time at regular intervals, it is not
|
|
|
|
|
important to follow any sequence. We just need to make sure that atleast
|
|
|
|
|
1 broker in the master/slave pair is live to take up the connections from
|
|
|
|
|
the client applications.
|
|
|
|
|
|
|
|
|
|
#### Note on restarting
|
|
|
|
|
> While restarting the brokers while the client applications are connected
|
|
|
|
|
kindly make sure that atleast one broker is always live to serve the connected
|
|
|
|
|
clients.
|
|
|
|
|
|
|
|
|
|
## Completely shutting down the brokers and starting
|
|
|
|
|
If there is situation that we need to completely shutdown the brokers and
|
|
|
|
|
start them again, please follow the following procedure:
|
|
|
|
|
|
|
|
|
|
1. Shut down all the slave brokers.
|
|
|
|
|
2. Shut down all the master brokers.
|
|
|
|
|
3. Start all the master brokers.
|
|
|
|
|
4. Start all the slave brokers.
|
|
|
|
|
|
|
|
|
|
This sequence is particularly important in case of network replication for
|
|
|
|
|
the following reasons:
|
|
|
|
|
If the master broker is shutdown first, the slave broker will come live and accept
|
|
|
|
|
all the client connections. Then when the slave broker is stopped, the clients will
|
|
|
|
|
remain connected to the last live connection i.e. slave. Now, when we start the slave
|
|
|
|
|
and master brokers, the clients will keep trying to connecting to the last connection
|
|
|
|
|
i.e. with slave and will never be able to connect until we restart the client applications.
|
|
|
|
|
To avoid the hassle of restarting of client applications, we must follow the sequence
|
|
|
|
|
as suggested above.
|
|
|
|
|
|
|
|
|
|
## Split-brain situation
|
|
|
|
|
The following procedure helps the cluster to recover from the split-brain situation
|
|
|
|
|
and getting the client connections auto-reconnected to the cluster.
|
|
|
|
|
With this sequence, client applications do not need to be restarted in order to make
|
|
|
|
|
connection with the brokers.
|
|
|
|
|
|
|
|
|
|
During the split brain situation both the master and slave brokers are live and there is
|
|
|
|
|
no replication that is happening from the master broker to the slave.
|
|
|
|
|
|
|
|
|
|
In such situation, there can be some client applications that are connected to the master
|
|
|
|
|
broker and other connected to the slave broker. Now after we restart the brokers and the
|
2020-12-07 13:49:13 -05:00
|
|
|
cluster is properly formed.
|
2020-02-04 23:02:32 -05:00
|
|
|
|
|
|
|
|
Here, the clients that were connected to the master broker during the split brain situation
|
|
|
|
|
are auto-connected to the cluster and start processing the messages. But the clients that got
|
|
|
|
|
connected to the slave broker are still trying to make connection with the broker. This happens
|
|
|
|
|
because the slave broker has restarted in 'back up' mode.
|
|
|
|
|
|
|
|
|
|
Thus, not all the clients get connected to the brokers and function properly.
|
|
|
|
|
|
|
|
|
|
To avoid such mishap, kindly follow the below sequence:
|
|
|
|
|
1. Stop the slave broker
|
|
|
|
|
2. Start the slave broker. Observe the logs for the message "Waiting for the master"
|
|
|
|
|
3. Stop the master broker.
|
|
|
|
|
4. Start the master broker.
|
|
|
|
|
Observe the master broker logs for "Server is live"
|
|
|
|
|
Observe the slave broker logs for "backup announced"
|
|
|
|
|
5. Stop the master broker again. Wait until the slave broker becomes live. Observe that all the
|
|
|
|
|
clients are connected to the slave broker.
|
|
|
|
|
6. Start the master broker. This time, all the connections will be switched to master broker again,
|
|
|
|
|
|
|
|
|
|
#### Note on delta message loss on the slave broker
|
|
|
|
|
|
|
|
|
|
> During the split brain situation, messages are produced on the slave broker since it is live.
|
|
|
|
|
While resolving the split brain situation, if there are some delta messages that are not produced
|
|
|
|
|
on the slave broker. Those messages cannot be auto-recovered. There will be manual intervention
|
|
|
|
|
required to retrieve the messages, sometime it is almost impossible to recover the messages.
|
|
|
|
|
> The above mentioned sequence helps in forming the cluster that was broken due to split brain
|
|
|
|
|
and getting all the client applications to auto connected to the cluster without any need for
|
|
|
|
|
client applications to be restarted.
|
