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| <h1>Multipoint (TCP) Discovery |
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| |
| <p>As TCP has no real broadcast functionality to speak of, communication of |
| who is in the network is achieved by each server having a physical |
| connection to each other server in the network.</p> |
| |
| <p>To join the network, the server must be configured to know the address of |
| at least one server in the network and connect to it. When it does both |
| servers will exchange the full list of all the other servers each knows |
| about. Each server will then connect to any new servers they've just |
| learned about and repeat the processes with those new servers. The end |
| result is that everyone has a direct connection to everyone 100% of the |
| time, hence the made-up term "multipoint" to describe this situation of |
| each server having multiple point-to-point connections which create a fully |
| connected graph.</p> |
| |
| <p>On the client side things are similar. It needs to know the address of at |
| least one server in the network and be able to connect to it. When it does |
| it will get the full (and dynamically maintained) list of every server in |
| the network. The client doesn't connect to each of those servers |
| immediately, but rather consults the list in the event of a failover, using |
| it to decide who to connect to next.</p> |
| |
| <p>The entire process is essentially the art of using a statically maintained |
| list to bootstrap getting the more valuable dynamically maintained list.</p> |
| |
| <h1>Server Configuration</h1> |
| |
| <p>In the server this list can be specified via the |
| <code>conf/multipoint.properties</code> file like so:</p> |
| |
| <pre><code>server = org.apache.openejb.server.discovery.MultipointDiscoveryAgent |
| bind = 127.0.0.1 |
| port = 4212 |
| disabled = false |
| initialServers = 192.168.1.20:4212, 192.168.1.30:4212, 192.168.1.40:4212 |
| </code></pre> |
| |
| <p>The above configuration shows the server has an <code>port</code> <code>4212</code> open for |
| connections by other servers for multipoint communication. The |
| <code>initialServers</code> list should be a comma separated list of other similar |
| servers on the network. Only one of the servers listed is required to be |
| running when this server starts up -- it is not required to list all |
| servers in the network.</p> |
| |
| <h1>Client Configuration</h1> |
| |
| <p>Configuration in the client is similar, but note that EJB clients do not |
| participate directly in multipoint communication and do <strong>not</strong> connect to |
| the multipoint port. The server list is simply a list of the regular |
| <code>ejbd://</code> urls that a client normally uses to connect to a server.</p> |
| |
| <pre><code>Properties p = new Properties(); |
| p.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory"); |
| p.put(Context.PROVIDER_URL, "failover:ejbd://192.168.1.20:4201,ejbd://192.168.1.30:4201"); |
| InitialContext remoteContext = new InitialContext(p); |
| </code></pre> |
| |
| <p>Failover can work entirely driven by the server, the client does not need |
| to be configured to participate. A client can connect as usual to the server.</p> |
| |
| <pre><code>Properties p = new Properties(); |
| p.put(Context.INITIAL_CONTEXT_FACTORY, "org.apache.openejb.client.RemoteInitialContextFactory"); |
| p.put(Context.PROVIDER_URL, "ejbd://192.168.1.20:4201"); |
| InitialContext remoteContext = new InitialContext(p); |
| </code></pre> |
| |
| <p>If the server at <code>192.168.1.20:4201</code> supports failover, so will the client.</p> |
| |
| <p>In this scenario the list of servers used for failover is supplied entirely |
| by the server at <code>192.168.1.20:4201</code>. The server could have aquired the list |
| via multicast or multipoint (or both), but this detail is not visible to the |
| client.</p> |
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