72a3ed6b5f
Changing travis link in README Removed maven section from readme Adding NOTICE file in project Adding DISCLAIMER file in codebase
109 lines
3.1 KiB
Markdown
109 lines
3.1 KiB
Markdown
# Gossip 
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Gossip protocol is a method for a group of nodes to discover and check the liveliness of a cluster. More information can be found at http://en.wikipedia.org/wiki/Gossip_protocol.
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The original implementation was forked from https://code.google.com/p/java-gossip/. Several bug fixes and changes have already been added.
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Usage
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-----
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To gossip you need one or more seed nodes. Seed is just a list of places to initially connect to.
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```java
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GossipSettings settings = new GossipSettings();
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int seedNodes = 3;
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List<GossipMember> startupMembers = new ArrayList<>();
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for (int i = 1; i < seedNodes+1; ++i) {
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startupMembers.add(new RemoteGossipMember("127.0.0." + i, 2000, i + ""));
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}
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```
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Here we start five gossip processes and check that they discover each other. (Normally these are on different hosts but here we give each process a distinct local ip.
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```java
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List<GossipService> clients = new ArrayList<>();
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int clusterMembers = 5;
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for (int i = 1; i < clusterMembers+1; ++i) {
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GossipService gossipService = new GossipService("127.0.0." + i, 2000, i + "",
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LogLevel.DEBUG, startupMembers, settings, null);
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clients.add(gossipService);
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gossipService.start();
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}
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```
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Later we can check that the nodes discover each other
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```java
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Thread.sleep(10000);
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for (int i = 0; i < clusterMembers; ++i) {
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Assert.assertEquals(4, clients.get(i).get_gossipManager().getMemberList().size());
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}
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```
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Usage with Settings File
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-----
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For a very simple client setup with a settings file you first need a JSON file such as:
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```json
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[{
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"id":"419af818-0114-4c7b-8fdb-952915335ce4",
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"port":50001,
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"gossip_interval":1000,
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"cleanup_interval":10000,
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"members":[
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{"host":"127.0.0.1", "port":50000}
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]
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}]
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```
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where:
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* `id` - is a unique id for this node (you can use any string, but above we use a UUID)
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* `port` - the port to use on the default adapter on the node's machine
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* `gossip_interval` - how often (in milliseconds) to gossip list of members to other node(s)
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* `cleanup_interval` - when to remove 'dead' nodes (in milliseconds)
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* `members` - initial seed nodes
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Then starting a local node is as simple as:
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```java
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GossipService gossipService = new GossipService(
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StartupSettings.fromJSONFile( "node_settings.json" )
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);
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gossipService.start();
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```
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And then when all is done, shutdown with:
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```java
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gossipService.shutdown();
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```
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Event Listener
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------
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The status can be polled using the getters that return immutable lists.
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```java
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List<LocalGossipMember> getMemberList()
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public List<LocalGossipMember> getDeadList()
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```
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These can be accessed from the `GossipManager` on your `GossipService`, e.g:
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`gossipService.get_gossipManager().getMemberList();`
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Users can also attach an event listener:
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```java
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GossipService gossipService = new GossipService("127.0.0." + i, 2000, i + "", LogLevel.DEBUG,
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startupMembers, settings,
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new GossipListener(){
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@Override
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public void gossipEvent(GossipMember member, GossipState state) {
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System.out.println(member+" "+ state);
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}
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});
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```
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