09 JobManager 高可用安装（HA)

JobManager High Availability (HA)

The JobManager is the coordinator of each Flink deployment. It is responsible for both scheduling and resource management.
By default, there is a single JobManager instance per Flink cluster. This creates a single point of failure (SPOF): if the JobManager crashes, no new programs can be submitted and running programs
fail.
With JobManager High Availability, you can run multiple JobManager instances per Flink cluster and thereby circumvent the SPOF.
The general idea of JobManager high availability is that there is a single leading JobManager at any time and multiple standby JobManagers to
take over leadership in case the leader fails. This guarantees that there is no single point of failure and programs can make progress as soon as a standby JobManager has taken leadership. There is no explicit distinction
between standby and master JobManager instances. Each JobManager can take the role of master or standby.
As an example, consider the following setup with three JobManager instances:

Configuration

To enable JobManager High Availability you have to set the recovery mode to zookeeper, configure a ZooKeeper quorum and
set up a masters file with all JobManagers hosts and their web ui ports.
Flink leverages ZooKeeper for distributed
coordination between all running JobManager instances. ZooKeeper is a separate service from Flink, which provides highly reliable distirbuted coordination via leader election and light-weight consistent state storage. Check out ZooKeeper’s
Getting Started Guide for more information about ZooKeeper.
Setting Flink’s recovery mode to zookeeper in

conf/flink-conf.yaml

enables high
availability mode.
Additionally, you have to configure a ZooKeeper quorum in the same configuration file.
In high availabliity mode, all Flink components try to connect to a JobManager via coordination through ZooKeeper.

Recovery mode (required): The recovery mode has to be set in

conf/flink-conf.yaml

to zookeeper in
order to enable high availability mode.

recovery.mode: zookeeper

ZooKeeper quorum (required): A ZooKeeper quorum is a replicated group of ZooKeeper servers, which provide the distributed coordination service.

recovery.zookeeper.quorum: address1:2181[,...],addressX:2181

Each addressX:port refers to a ZooKeeper server, which is reachable by Flink at the given address and port.

The following configuration keys are optional:

recovery.zookeeper.path.root: /flink [default]

: ZooKeeper directory to use for coordination
TODO Add client configuration keys

Starting an HA-cluster

In order to start an HA-cluster configure the masters file in

conf/masters

:

masters file: The masters file contains all hosts, on which JobManagers are started, and the ports to which the web user interface binds.

jobManagerAddress1:webUIPort1
[...]
jobManagerAddressX:webUIPortX

After configuring the masters and the ZooKeeper quorum, you can use the provided cluster startup scripts as usual. They will start a HA-cluster.Keep in mind that the ZooKeeper quorum
has to be running when you call the scripts.

Running ZooKeeper

If you don’t have a running ZooKeeper installation, you can use the helper scripts, which ship with Flink.
There is a ZooKeeper configuration template in

conf/zoo.cfg

. You can configure
the hosts to run ZooKeeper on with the

server.X

entries, where X is a unique ID of each server:

server.X=addressX:peerPort:leaderPort
[...]
server.Y=addressY:peerPort:leaderPort

The script

bin/start-zookeeper-quorum.sh

will start a ZooKeeper server on
each of the configured hosts. The started processes start ZooKeeper servers via a Flink wrapper, which reads the configuration from

conf/zoo.cfg

and
makes sure to set some required configuration values for convenience. In production setups, it is recommended to manage your own ZooKeeper installation.

Example: Start and stop a local HA-cluster with 2 JobManagers

Configure recovery mode and ZooKeeper quorum in

conf/flink.yaml

:

recovery.mode: zookeeper
recovery.zookeeper.quorum: localhost

Configure masters in

conf/masters

:

localhost:8081
localhost:8082

Configure ZooKeeper server in

conf/zoo.cfg

(currently
it’s only possible to run a single ZooKeeper server per machine):

server.0=localhost:2888:3888

Start ZooKeeper quorum:

$ bin/start-zookeeper-quorum.sh
Starting zookeeper daemon on host localhost.

Start an HA-cluster:

$ bin/start-cluster-streaming.sh
Starting HA cluster (streaming mode) with 2 masters and 1 peers in ZooKeeper quorum.
Starting jobmanager daemon on host localhost.
Starting jobmanager daemon on host localhost.
Starting taskmanager daemon on host localhost.

Stop ZooKeeper quorum and cluster:

$ bin/stop-cluster.sh
Stopping taskmanager daemon (pid: 7647) on localhost.
Stopping jobmanager daemon (pid: 7495) on host localhost.
Stopping jobmanager daemon (pid: 7349) on host localhost.
$ bin/stop-zookeeper-quorum.sh
Stopping zookeeper daemon (pid: 7101) on host localhost.