ZooKeeper component Asciidoc documentation
Project: http://git-wip-us.apache.org/repos/asf/camel/repo Commit: http://git-wip-us.apache.org/repos/asf/camel/commit/d4f63390 Tree: http://git-wip-us.apache.org/repos/asf/camel/tree/d4f63390 Diff: http://git-wip-us.apache.org/repos/asf/camel/diff/d4f63390 Branch: refs/heads/master Commit: d4f633903fb6405b2336a753231032412f99d21d Parents: 8300779 Author: Antonin Stefanutti <anto...@stefanutti.fr> Authored: Thu Jan 28 18:26:31 2016 +0100 Committer: Claus Ibsen <davscl...@apache.org> Committed: Thu Jan 28 19:06:27 2016 +0100 ---------------------------------------------------------------------- .../src/main/docs/zookeeper.adoc | 254 +++++++++++++++++++ docs/user-manual/en/SUMMARY.md | 1 + 2 files changed, 255 insertions(+) ---------------------------------------------------------------------- http://git-wip-us.apache.org/repos/asf/camel/blob/d4f63390/components/camel-zookeeper/src/main/docs/zookeeper.adoc ---------------------------------------------------------------------- diff --git a/components/camel-zookeeper/src/main/docs/zookeeper.adoc b/components/camel-zookeeper/src/main/docs/zookeeper.adoc new file mode 100644 index 0000000..c4c13d0 --- /dev/null +++ b/components/camel-zookeeper/src/main/docs/zookeeper.adoc @@ -0,0 +1,254 @@ +[[Zookeeper-ZooKeeper]] +ZooKeeper +~~~~~~~~~ + +*Available as of Camel 2.9* + +The ZooKeeper component allows interaction with a +http://hadoop.apache.org/zookeeper/[ZooKeeper] cluster and exposes the +following features to Camel: + +1. Creation of nodes in any of the ZooKeeper create modes. +2. Get and Set the data contents of arbitrary cluster nodes (data +being set must be convertible to `byte[]`). +3. Create and retrieve the list the child nodes attached to a +particular node. +4. A Distributed link:routepolicy.html[`RoutePolicy`] that leverages a +Leader election coordinated by ZooKeeper to determine if exchanges +should get processed. + +Maven users will need to add the following dependency to their `pom.xml` +for this component: + +[source,xml] +---- +<dependency> + <groupId>org.apache.camel</groupId> + <artifactId>camel-zookeeper</artifactId> + <version>x.x.x</version> + <!-- use the same version as your Camel core version --> +</dependency> +---- + +[[Zookeeper-URIformat]] +URI format +^^^^^^^^^^ + +[source] +---- +zookeeper://zookeeper-server[:port][/path][?options] +---- + +The path from the URI specifies the node in the ZooKeeper server (a.k.a. +_znode_) that will be the target of the endpoint: + +[[Zookeeper-Options]] +Options +^^^^^^^ + +// endpoint options: START +The ZooKeeper component supports 14 endpoint options which are listed below: + +[width="100%",cols="2s,1,1m,1m,5",options="header"] +|======================================================================= +| Name | Group | Default | Java Type | Description +| serverUrls | common | | String | *Required* The zookeeper server hosts (multiple servers can be separated by comma) +| path | common | | String | *Required* The node in the ZooKeeper server (aka znode) +| awaitExistence | common | true | boolean | Not in use +| listChildren | common | false | boolean | Whether the children of the node should be listed +| timeout | common | 5000 | int | The time interval to wait on connection before timing out. +| backoff | consumer | 5000 | long | The time interval to backoff for after an error before retrying. +| bridgeErrorHandler | consumer | false | boolean | Allows for bridging the consumer to the Camel routing Error Handler which mean any exceptions occurred while the consumer is trying to pickup incoming messages or the likes will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions that will be logged at WARN/ERROR level and ignored. +| repeat | consumer | false | boolean | Should changes to the znode be 'watched' and repeatedly processed. +| sendEmptyMessageOnDelete | consumer | true | boolean | Upon the delete of a znode should an empty message be send to the consumer +| exceptionHandler | consumer (advanced) | | ExceptionHandler | To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this options is not in use. By default the consumer will deal with exceptions that will be logged at WARN/ERROR level and ignored. +| create | producer | false | boolean | Should the endpoint create the node if it does not currently exist. +| createMode | producer | EPHEMERAL | String | The create mode that should be used for the newly created node +| exchangePattern | advanced | InOnly | ExchangePattern | Sets the default exchange pattern when creating an exchange +| synchronous | advanced | false | boolean | Sets whether synchronous processing should be strictly used or Camel is allowed to use asynchronous processing (if supported). +|======================================================================= +// endpoint options: END + +[[Zookeeper-Usecases]] +Use cases +^^^^^^^^^ + +[[Zookeeper-Readingfromaznode]] +Reading from a _znode_ ++++++++++++++++++++++ + +The following snippet will read the data from the _znode_ +`/somepath/somenode/` provided that it already exists. The data +retrieved will be placed into an exchange and passed onto +the rest of the route: + +[source,java] +---- +from("zookeeper://localhost:39913/somepath/somenode").to("mock:result"); +---- + +If the node does not yet exist then a flag can be supplied to have the +endpoint await its creation: + +[source,java] +---- +from("zookeeper://localhost:39913/somepath/somenode?awaitCreation=true").to("mock:result"); +---- + +[[Zookeeper-ReadingfromaznodeAdditionalCamel210onwards]] +Reading from a _znode_ (additional Camel 2.10 onwards) +++++++++++++++++++++++++++++++++++++++++++++++++++++++ + +When data is read due to a `WatchedEvent` received from the ZooKeeper +ensemble, the `CamelZookeeperEventType` header holds ZooKeeper's +http://zookeeper.apache.org/doc/current/api/org/apache/zookeeper/Watcher.Event.EventType.html[`EventType`] +value from that `WatchedEvent`. If the data is read initially (not +triggered by a `WatchedEvent`) the `CamelZookeeperEventType` header will not +be set. + +[[Zookeeper-Writingtoaznode]] +Writing to a _znode_ +++++++++++++++++++++ + +The following snippet will write the payload of the exchange into the +znode at `/somepath/somenode/` provided that it already exists: + +[source,java] +---- +from("direct:write-to-znode") + .to("zookeeper://localhost:39913/somepath/somenode"); +---- + +For flexibility, the endpoint allows the target _znode_ to be specified +dynamically as a message header. If a header keyed by the string +`CamelZooKeeperNode` is present then the value of the header will be +used as the path to the _znode_ on the server. For instance using the same +route definition above, the following code snippet will write the data +not to `/somepath/somenode` but to the path from the header +`/somepath/someothernode`. + +WARNING: the `testPayload` must be convertible +to `byte[]` as the data stored in ZooKeeper is byte based. + +[source,java] +---- +Object testPayload = ... +template.sendBodyAndHeader("direct:write-to-znode", testPayload, "CamelZooKeeperNode", "/somepath/someothernode"); +---- + +To also create the node if it does not exist the `create` option should +be used. + +[source,java] +---- +from("direct:create-and-write-to-znode") + .to("zookeeper://localhost:39913/somepath/somenode?create=true"); +---- + +Starting *version 2.11* it is also possible to *delete* a node using the +header `CamelZookeeperOperation` by setting it to `DELETE`: + +[source,java] +---- +from("direct:delete-znode") + .setHeader(ZooKeeperMessage.ZOOKEEPER_OPERATION, constant("DELETE")) + .to("zookeeper://localhost:39913/somepath/somenode"); +---- + +or equivalently: + +[source,xml] +---- +<route> + <from uri="direct:delete-znode" /> + <setHeader headerName="CamelZookeeperOperation"> + <constant>DELETE</constant> + </setHeader> + <to uri="zookeeper://localhost:39913/somepath/somenode" /> +</route> +---- + +ZooKeeper nodes can have different types; they can be 'Ephemeral' or +'Persistent' and 'Sequenced' or 'Unsequenced'. For further information +of each type you can check +http://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html#Ephemeral+Nodes[here]. +By default endpoints will create unsequenced, ephemeral nodes, but the +type can be easily manipulated via a uri config parameter or via a +special message header. The values expected for the create mode are +simply the names from the `CreateMode` enumeration: + +* `PERSISTENT` +* `PERSISTENT_SEQUENTIAL` +* `EPHEMERAL` +* `EPHEMERAL_SEQUENTIAL` + +For example to create a persistent _znode_ via the URI config: + +[source,java] +---- +from("direct:create-and-write-to-persistent-znode") + .to("zookeeper://localhost:39913/somepath/somenode?create=true&createMode=PERSISTENT"); +---- + +or using the header `CamelZookeeperCreateMode`. + +WARNING: the `testPayload` must be convertible to `byte[]` as the data stored in +ZooKeeper is byte based. + +[source,java] +---- +Object testPayload = ... +template.sendBodyAndHeader("direct:create-and-write-to-persistent-znode", testPayload, "CamelZooKeeperCreateMode", "PERSISTENT"); +---- + +[[Zookeeper-ZooKeeperenabledRoutepolicy]] +ZooKeeper enabled Route policy +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +ZooKeeper allows for very simple and effective leader election out of +the box. This component exploits this election capability in a +link:routepolicy.html[`RoutePolicy`] to control when and how routes are +enabled. This policy would typically be used in fail-over scenarios, to +control identical instances of a route across a cluster of Camel based +servers. A very common scenario is a simple 'Master-Slave' setup where +there are multiple instances of a route distributed across a cluster but +only one of them, that of the master, should be running at a time. If +the master fails, a new master should be elected from the available +slaves and the route in this new master should be started. + +The policy uses a common _znode_ path across all instances of the +`RoutePolicy` that will be involved in the election. Each policy writes +its id into this node and Zookeeper will order the writes in the order +it received them. The policy then reads the listing of the node to see +what position of its id; this position is used to determine if the route +should be started or not. The policy is configured at startup with the +number of route instances that should be started across the cluster and +if its position in the list is less than this value then its route will +be started. For a Master-slave scenario, the route is configured with 1 +route instance and only the first entry in the listing will start its +route. All policies watch for updates to the listing and if the listing +changes they recalculate if their route should be started. For more info +on Zookeeper's leader election capability see +http://zookeeper.apache.org/doc/trunk/recipes.html#sc_leaderElection[this +page]. + +The following example uses the node `/someapplication/somepolicy` for +the election and is set up to start only the top '1' entries in the node +listing i.e. elect a master: + +[source,java] +---- +ZooKeeperRoutePolicy policy = new ZooKeeperRoutePolicy("zookeeper:localhost:39913/someapp/somepolicy", 1); +from("direct:policy-controlled") + .routePolicy(policy) + .to("mock:controlled"); +---- + +[[Zookeeper-SeeAlso]] +See Also +^^^^^^^^ + +* link:configuring-camel.html[Configuring Camel] +* link:component.html[Component] +* link:endpoint.html[Endpoint] +* link:getting-started.html[Getting Started] http://git-wip-us.apache.org/repos/asf/camel/blob/d4f63390/docs/user-manual/en/SUMMARY.md ---------------------------------------------------------------------- diff --git a/docs/user-manual/en/SUMMARY.md b/docs/user-manual/en/SUMMARY.md index 4efcd7d..8ed8d9a 100644 --- a/docs/user-manual/en/SUMMARY.md +++ b/docs/user-manual/en/SUMMARY.md @@ -104,6 +104,7 @@ * [SJMS](sjms.adoc) * [SJMS Batch](sjms-batch.adoc) * [Twitter](twitter.adoc) + * [ZooKeeper](zookeeper.adoc) <!-- * [Expession Languages](languages.adoc)
