Heron relies on ZooKeeper for a wide variety of cluster coordination tasks. You can use either a shared or dedicated ZooKeeper cluster.
There are a few things you should be aware of regarding Heron and ZooKeeper:
- Heron uses ZooKeeper only for coordination, not for message passing, which means that ZooKeeper load should generally be fairly low. A single-node and/or shared ZooKeeper may suffice for your Heron cluster, depending on usage.
- Heron uses ZooKeeper more efficiently than Storm. This makes Heron less likely than Storm to require a bulky or dedicated ZooKeeper cluster, but your use case may require one.
- We strongly recommend running ZooKeeper under supervision.
ZooKeeper State Manager Configuration
You can make Heron aware of the ZooKeeper cluster by modifying the
statemgr.yaml config file specific for the Heron cluster. You’ll
need to specify the following for each cluster:
heron.class.state.manager— Indicates the class to be loaded for managing the state in ZooKeeper and this class is loaded using reflection. You should set this to
heron.statemgr.connection.string— The host IP address and port to connect to ZooKeeper cluster (e.g) “127.0.0.1:2181”.
heron.statemgr.root.path— The root ZooKeeper node to be used by Heron. We recommend providing Heron with an exclusive root node; if you do not, make sure that the following child nodes are unused:
heron.statemgr.zookeeper.is.initialize.tree— Indicates whether the nodes under ZooKeeper root
/schedulersneed to created, if they are not found. Set it to
Trueif you could like Heron to create those nodes. If those nodes are already there, set it to
False. The absence of this configuration implies
heron.statemgr.zookeeper.session.timeout.ms— Specifies how much time in milliseconds to wait before declaring the ZooKeeper session is dead.
heron.statemgr.zookeeper.connection.timeout.ms— Specifies how much time in milliseconds to wait before the connection to ZooKeeper is dead.
heron.statemgr.zookeeper.retry.count— Count of the number of retry attempts to connect to ZooKeeper
heron.statemgr.zookeeper.retry.interval.ms: Time in milliseconds to wait between each retry
Example ZooKeeper State Manager Configuration
Below is an example configuration (in
statemgr.yaml) for a ZooKeeper running in
# local state manager class for managing state in a persistent fashion heron.class.state.manager: com.twitter.heron.statemgr.zookeeper.curator.CuratorStateManager # local state manager connection string heron.statemgr.connection.string: "127.0.0.1:2181" # path of the root address to store the state in a local file system heron.statemgr.root.path: "/heron" # create the zookeeper nodes, if they do not exist heron.statemgr.zookeeper.is.initialize.tree: True # timeout in ms to wait before considering zookeeper session is dead heron.statemgr.zookeeper.session.timeout.ms: 30000 # timeout in ms to wait before considering zookeeper connection is dead heron.statemgr.zookeeper.connection.timeout.ms: 30000 # timeout in ms to wait before considering zookeeper connection is dead heron.statemgr.zookeeper.retry.count: 10 # duration of time to wait until the next retry heron.statemgr.zookeeper.retry.interval.ms: 10000