THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
ZooKeeper
Available as of Camel
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2.9
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The
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ZooKeeper
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component
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allows
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interaction
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with
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a
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cluster
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and
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exposes
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the
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following
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features
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to
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Camel:
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- Creation
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- of
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- nodes
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- in
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- any
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- of
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- the
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- ZooKeeper
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- create
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- modes.
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- Get
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- and
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- Set
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- the
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- data
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- contents
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- of
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- arbitrary
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- cluster
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- nodes. (data being set must be convertable to byte[])
- Create and retrieve the list the child nodes attached to a particular node.
- A Distributed 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:
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# Create and retrieve the list the child nodes attached to a particular node. # A Distributed [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: {code: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> {code} h3. URI format {code} |
URI format
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zookeeper://zookeeper-server[:port][/path][?options]
{code}
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The
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path
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from
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the
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uri
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specifies
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the
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node
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in
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the
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ZooKeeper
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server
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(aka
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znode)
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that
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will
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be
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the
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target
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of
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the
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endpoint.
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Options
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Use cases
Reading from a znode.
The following snippet will read the data from the znode '/somepath/somenode/'
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provided
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that
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it
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already
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exists.
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The
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data
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retrieved
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will
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be
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placed
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into
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an
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exchange
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and
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passed
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onto
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the
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rest
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of
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the
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route.
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{code:java} from("zookeeper://localhost:39913/somepath/somenode").to("mock:result"); {code} |
if
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the
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node
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does
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not
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yet
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exist
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then
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a
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flag
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can
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be
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supplied
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to
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have
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the
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endpoint
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await
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its
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creation
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{code:java} from("zookeeper://localhost:39913/somepath/somenode?awaitCreation=true").to("mock:result"); {code} h4. Reading from a znode - (additional Camel |
Reading from a znode - (additional Camel 2.10
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onwards)
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When
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data
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is
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read
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due
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to
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a
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WatchedEvent
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received
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from
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the
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ZooKeeper
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ensemble,
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the
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CamelZookeeperEventType
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header
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holds
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ZooKeeper's
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value
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from
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that
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WatchedEvent.
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If
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the
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data
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is
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read
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initially
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(not
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triggered
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by
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a
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WatchedEvent)
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the
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CamelZookeeperEventType
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header
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will
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not
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be
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set.
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Writing to a znode.
The following snippet will write the payload of the exchange into the znode at '/somepath/somenode/'
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provided
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that
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it
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already
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exists
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{code:java} from("direct:write-to-znode").to("zookeeper://localhost:39913/somepath/somenode"); {code} |
For
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flexibility,
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the
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endpoint
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allows
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the
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target
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znode
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to
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be
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specified
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dynamically
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as
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a
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message
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header.
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If
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a
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header
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keyed
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by
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the
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string
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'CamelZooKeeperNode'
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is
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present
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then
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the
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value
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of
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the
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header
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will
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be
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used
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as
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the
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path
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to
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the
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znode
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on
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the
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server.
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For
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instance
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using
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the
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same
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route
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definition
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above,
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the
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following
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code
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snippet
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will
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write
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the
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data
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not
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to
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'/somepath/somenode'
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but
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to
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the
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path
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from
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the
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header
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'/somepath/someothernode'. Notice the testPayload must be convertable to byte[] as the data stored in ZooKeeper is byte based.
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Object testPayload = ... {code:java} Exchange e = createExchangeWithBody(testPayload); template.sendBodyAndHeader("direct:write-to-znode", etestPayload, "CamelZooKeeperNode", "/somepath/someothernode"); {code} |
To
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also
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create
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the
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node
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if
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it
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does
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not
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exist
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the
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'create'
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option
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should
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be
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used.
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{code:java} from("direct:create-and-write-to-znode").to("zookeeper://localhost:39913/somepath/somenode?create=true"); {code} ZooKeeper nodes can have different types; they can be 'Ephemeral' or 'Persistent' and 'Sequenced' or 'Unsequenced |
Starting version 2.11 it is also possible to delete a node using the header 'CamelZookeeperOperation' by setting it to 'DELETE'.
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from("direct:delete-znode").setHeader(ZooKeeperMessage.ZOOKEEPER_OPERATION, constant("DELETE")).to("zookeeper://localhost:39913/somepath/somenode");
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or equivalently
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<route>
<from uri="direct:delete-znode" />
<setHeader headerName="CamelZookeeperOperation">
<constant>DELETE</constant>
</setHeader>
<to uri="zookeeper://localhost:39913/somepath/somenode" />
</route>
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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 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
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'. For further information of each type you can check [here|http://zookeeper.apache.org/doc/trunk/zookeeperProgrammers.html#Ephemeral+Nodes]. 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 {code:java} from("direct:create-and-write-to-persistent-znode").to("zookeeper://localhost:39913/somepath/somenode?create=true&createMode=PERSISTENT"); {code} |
or
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using
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the
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header
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'CamelZookeeperCreateMode'. Notice the testPayload must be convertable to byte[] as the data stored in ZooKeeper is byte based.
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Object testPayload = ... {code:java} Exchange e = createExchangeWithBody(testPayload); template.sendBodyAndHeader("direct:create-and-write-to-persistent-znode", etestPayload, "CamelZooKeeperCreateMode", "PERSISTENT"); |
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 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 postion of its id; this postion 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 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
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{code} h3. 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 [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 postion of its id; this postion 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] 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 {code:java} ZooKeeperRoutePolicy policy = new ZooKeeperRoutePolicy("zookeeper:localhost:39913/someapp/somepolicy", 1); from("direct:policy-controlled").routePolicy(policy).to("mock:controlled"); {code} {include:Endpoint See Also} |
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