The required conf/zoo.cfg file for replicated mode is similar to the one used in standalone mode, but with a few differences. Two servers are inherently less stable than a single server, because there are two single points of failure. If you only have two servers, then you are in a situation where if one of them fails, there are not enough machines to form a majority quorum. Noteįor replicated mode, a minimum of three servers are required, and it is strongly recommended that you have an odd number of servers. A replicated group of servers in the same application is called a quorum, and in replicated mode, all servers in the quorum have copies of the same configuration file. But in production, you should run ZooKeeper in replicated mode. Running ZooKeeper in standalone mode is convenient for evaluation, some development, and testing. For more information, see the Programming Examples in the ZooKeeper Programmer's Guide for sample code using the different APIs. These differ only in how the messaging loop is done. The C bindings exist in two variants: single threaded and multi-threaded. ZooKeeper has a Java bindings and C bindings. (Notice we did a get after setting the data and it did, indeed, change.įinally, let's delete the node by issuing: delete /zk_test We can change the data associated with zk_test by issuing the set command, as in: set /zk_test junk Next, verify that the data was associated with the znode by running the get command, as in: get /zk_test Notice that the zk_test directory has now been created. Issue another ls / command to see what the directory looks like: ls / This creates a new znode and associates the string "my_data" with the node. Next, create a new znode by running create /zk_test my_data. First, start by issuing the list command, as in ls, yielding: ls / Reconfig | *]] | ]* *]įrom here, you can try a few simple commands to get a feel for this simple command line interface. Once you have connected, you should see something like: Connecting to localhost:2181įrom the shell, type help to get a listing of commands that can be executed from the client, as in: helpĬreate path This lets you perform simple, file-like operations. See the section on maintenance for more details.Ĭonnecting to ZooKeeper $ bin/zkCli.sh -server 127.0.0.1:2181 This is fine for most development situations, but to run ZooKeeper in replicated mode, please see Running Replicated ZooKeeper.įor long running production systems ZooKeeper storage must be managed externally (dataDir and logs). There is no replication, so if ZooKeeper process fails, the service will go down. The steps outlined here run ZooKeeper in standalone mode. You will see log messages coming to the console (default) and/or a log file depending on the logback configuration. ZooKeeper logs messages using logback - more detail available in the Logging section of the Programmer's Guide. Now that you created the configuration file, you can start ZooKeeper: bin/zkServer.sh start It is used to do heartbeats and the minimum session timeout will be twice the tickTime.ĭataDir : the location to store the in-memory database snapshots and, unless specified otherwise, the transaction log of updates to the database.ĬlientPort : the port to listen for client connections TickTime : the basic time unit in milliseconds used by ZooKeeper. Here are the meanings for each of the fields: Change the value of dataDir to specify an existing (empty to start with) directory. This file can be called anything, but for the sake of this discussion call it conf/zoo.cfg. Here is a sample, create it in conf/zoo.cfg: tickTime=2000 To start ZooKeeper you need a configuration file. Once you've downloaded a stable ZooKeeper release unpack it and cd to the root The server is contained in a single JAR file, so installation consists of creating a configuration. Setting up a ZooKeeper server in standalone mode is straightforward. To get a ZooKeeper distribution, download a recent stable release from one of the Apache Download Mirrors. See System Requirements in the Admin guide. However for the complete instructions for commercial deployments, please refer to the ZooKeeper Administrator's Guide. Finally, as a convenience, there are a few sections regarding more complicated installations, for example running replicated deployments, and optimizing the transaction log. It is aimed primarily at developers hoping to try it out, and contains simple installation instructions for a single ZooKeeper server, a few commands to verify that it is running, and a simple programming example. This document contains information to get you started quickly with ZooKeeper. Getting Started: Coordinating Distributed Applications with ZooKeeper Getting Started: Coordinating Distributed Applications with ZooKeeper.
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