c97c5ff810
* Also tweaked the `StartupSettings` so that it now reads in an `id` for the node, rather than just resulting in a blank `id`; * Moved some logging from stdout to log4j * Full `maven test` passing Arguably this would result in a version change, as the settings file format has changed and now requires an id field. However we could make it optional, but it seems odd to have nodes with no ids.
123 lines
3.3 KiB
Markdown
123 lines
3.3 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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Maven
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------
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You can get this software from maven central.
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```xml
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<dependency>
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<groupId>io.teknek</groupId>
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<artifactId>gossip</artifactId>
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<version>${pick_the_latest_version}</version>
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</dependency>
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```
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