[rabbitmq-discuss] How do you handle recovering from a faulty connection using RabbitMQ java client library?

[Peter Moberg]

Hi,

I'm interested in knowing how other people handle recovering from a faulty
connection using the official RabbitMQ java client library. We are using it
to connect our application servers to our RabbitMQ cluster and we have
implemented a few different ways to recover from a connection failure, but
non of them feel quite right.

Imagine this pseudo application:

public class OurClassThatStartsConsumers {
    Connection conn;

    public void start() {
        ConnectionFactory factory = new ConnectionFactory();
        factory.setUsername("someusername");
        factory.setPassword("somepassword");
        factory.setHost("somehost");
        conn = factory.newConnection();

        new Thread(new Consumer(conn.createChannel())).start();
    }
  }
class Consumer1 implements Runnable {
    public Consumer1(Channel channel) {
         this.channel = channel;
    }

    @Override
    public void run() {
        while (true) {
             ... consume incoming messages on the channel...
            // How do we handle that the connection dies?
        }
    }}

In the real world we have several hundreds of consumers. So what happens if
the connection dies? In the above example Consumer1 can not recover, when
the connection closes, the Channel also closes, a state from which we can
not recover. So lets look at some ways to solve this:

Solution A)

Let every consumer have their own connection and register the events that
triggers when the connection dies and then handle reconnecting.

Pros: It works

Cons:

   - Since we have a lot of consumers, we probably do not want that many
   connections.
   - We might possible have a lot of duplicated code for reconnecting to
   rabbit and handle reconnecting

Solution B)

Have each consumer use the same connection and subscribe to its connection
failure events.

Pros: Less connections than in Solution A

Cons: Since the connection is closed we need to reopen/replace it. The java
client library doesn't seem to provide a way to reopen the connection, so
we would have to replace it with a new connection and then somehow notify
all the consumers about this new connection and they would have to recreate
the channels and the consumers. Once again, a lot of logic that i don't
want to see in the consumer ends up there.

Solution C)

Wrap Connection and Channel classes is classes that handle the
re-connection logic, the consumer only needs to know about the
WrappedChannel class. On a connection failure the WrappedConnection with
deal with re-establishing the connection and once connected the
WrappedConnection will automatically create new Channels and register
consumers.

Pros: It work - this is actually the solution we are using today.

Cons: It feels like a hack, I think this is something that should be
handled more elegantly by the underlying library.

Maybe there is a much better way? The API documentation does not talk that
much about recovering from a faulty connection. Any input is appreciated :)


Thanks,

Peter
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