Deploying and configuring Hadoop and HBase across clusters is a complex task. In this article I will show what we do to make it easier, and share the deployment recipes that we use.
Before going into how we do things, here is the list of tools that we are using, and which I will mention in this article. I will try to put a link next to any tool-specific term, but you can always refer to its specific home-page for further reference.
- Hudson – this is a great CI server, and we are using it to build Hadoop, HBase, Zookeeper and more
- The Hudson Promoted Builds Plug-in – allows defining operations that run after the build has finished, manually or automatically
- Puppet – configuration management tool We don’t have a dedicated operations team to hand off a list of instructions on how we want our machines to look like. The operations team helping us just makes sure the servers are in the rack, networked and powered up, but once we have a set of IPs (usually from IPMI cards) we’re good to go ourselves. We are our own devops team, and as such we try to automate as much as possible, where possible, and using the tools above helps a lot.
When we started with hstack, we did everything manually – created users, tweaked system properties and deployed Hadoop/HBase. By far the most time consuming part was making sure the configuration files were the same on all machines. We wrote a basic shell script that we ran on the machine where we modified the configuration files and it would use scp to copy the files to the rest of the machines. Once the initial excitement wore off, we looked for a better way. The tools we looked at first were Chef and Puppet. We eventually chose Puppet which at the time was richer and much better maintained. We went through their site wiki for documentation, used the fantastic Pulling Strings with Puppet book and in under a week we had created puppet recipes that could take an empty machine and turn it into a hstack node. Any functionality that we decided to implement later on (like the NameNode High-availability recipe) got its own puppet manifests right from the start.
How we use Puppet
We tend to overuse puppet a bit, by using it as both our configuration management and deployment tool. To illustrate, these are the steps we take when deploying a new version of hstack to our cluster:
- Trigger a build in Hudson for Hadoop, HBase or anything else we want to deploy.
- We click a link next to the newly completed build to push the resulting archives to the Puppet Master repository.
- Using ssh, we start up the Puppet clients on each machine. In the future we want to keep them running at all times, but since we’re doing development on the current cluster, a running Puppet tends to mess with our tests (restarting daemons when we kill them for testing is an example).
- The last step is to trigger the change in the configuration. The Puppet Master pulls the configuration from a git repository, so we just have to change the version number and push the new file back to source control.
The heavy lifting in all of this process is done by Puppet – it figures out what nodes need to be upgraded, pushes the new archives, changes configuration files and restarts services. All in all you can just do the steps above, go for a coffee and when you come back the cluster is running the new version.
Right now we are open-sourcing on GitHub, puppet recipes for:
- creating the user under which the entire hstack runs.
- changing system settings, like the ssh keys, authorizing machines to talk to each other, aliases for hadoop and hbase executables, /tmp rules.
- standalone puppet module to deploy Hadoop
- standalone puppet module to configure the Hadoop NameNode in High-Availability mode via DRBD, heartbeat and mon. For more details on this recipe check out the cloudera blog post on this topic.
- standalone puppet module to deploy HBase
- standalone puppet module to deploy Zookeeper.
All of the above are what we use day-to-day, and have been tested on CentOS 5.3 with puppet 0.25.1 and 0.25.4. To use them you need a functional puppet master (see details on how to configure puppet’s daemons here). Once you have that working, drop the code from our repository on top of your puppet master, and read on for the various options of each module / recipe.
The repository contains the three typical puppet folders:
- manifests – aside from the mandatory sites.pp and nodes.pp files, our repository also stores in this folder some recipes that weren’t big enough to warrant a module, as well as some utility definitions.
- templates – this folder stores configuration templates for the user and system. Hadoop and HBase templates are stored with their respective modules. Here you will have to add your own ssh keys and tweak system variables
- modules – the bulk of the recipes lies here. A Puppet module is a self-contained unit that does one thing only. We named each folder by its purpose: hadoop, hbase, mon, zookeeper.
In order to do a full deployment using these recipes, your nodes have to include both the general user and system recipes, as well as the modules. To adapt the final outcome for your specific cluster setup there are a few variables that you can set, and which I will explain for each module in part.
Basic node setup
In this brief section I will explain what needs to be defined in the puppet recipe in order to perform basic setup of a machine (getting a dedicated user account to run hstack and setting the correct ssh permissions). The recipes we’re going to use are stored in the manifests/virtual.pp and manifests/environment.pp.
First up, adding a new user to the system. The recipe for creating users does not work fully out of the box – you need to give it your own ssh keys to use. To do so, replace the files under templates/ssh_keys/keys with actual content (they’re just dummy files right now). You might also want to change the password – you need to write the already encrypted version into manifests/virtual.pp. The default password is hadoop, although it might not seem so.
Another customization you can make is to the system settings. These are controlled through the environment.pp file. In this file you can change the maximum number of file descriptors (default 200.000), aliases for commands and the tmpwatch(http://linux.about.com/library/cmd/blcmdl8_tmpwatch.htm) deamon configuration.
Once this is done, you can add your first node, run the configuration and enjoy the results – a brand new user ready to take on Hadoop. :)
The hadoop module has options and configurations you need to change to make it suit your setup. The most important ones you need to take care of are: in the modules/hadoop/templates/conf/ folder you can create a sub-folder for each separate environment you want to manage. This allows you to keep completely different templates and use the same code to push them to their respective locations. This is where the hadoop (core, hdfs and map-reduce) configuration templates are stored. By default only the critical properties are filled in, some with values, but most are using variables (you can spot them by the <%= %> marks). These variables can be set on a per-node basis, but I just define a base-node with the common values and have all the other nodes in a cluster extend that. Some of the variables that you need to set are:
$hadoop_version– the version of hadoop to deploy. The recipes are assuming as version the part of the tar name after hadoop-. For example if your generated archive is called hadoop-core-0.21.0-31, the version is “core-0.21.0-31″. Another assumption is that the archive contains a folder with the same name, which will be unpacked in the user’s home (/home/hadoop) and then symlinked to the final
$HADOOP_HOMEdestination. This tactic allows you to retain all versions ever deployed, and you can easily switch back between them by just re-creating the symbolic link to an older folder.
$hadoop_home– final directory to which the unpacked hadoop will be symlinked to
$environment– match this with the subfolder in the templates/conf that you want to use
$hadoop_default_fs_name– the uri to the NameNode; this gets pushed into hdfs-site.xml and core-site.xml
$hadoop_namenode_dir– the folder where the NameNode stores its files
$hadoop_datastore– the folders where the datanode stores its files. This is expressed as a list:
$mapred_job_tracker– uri to the Hadoop Map-Reduce job-tracker.
$hadoop_mapred_local– the local folder where the TaskTrackers should store its files. This is also a list of folders.
Hadoop HDFS High Avalability
To use this you need to dedicate two machines to the NameNode role and set some other variables (on both machines):
$virtual_ip– the common IP address that both computers will be sharing
$hostname_primary | $hostname_secondary– the hostnames of the two machines to use
$ip_primary | $ip_secondary– the IP addresses of both machines
$disk_dev_primary | $disk_dev_secondary– the device to use as the starting partition for drbd
$hadoop_namenode_dir– where the namenode will store its files; this will also be the mount point for the newly created
A standalone zookeeper deployment is recommended for HBase. You should have at least 3 servers running zookeeper – if your cluster is low on load, you can just use 3 of your regionservers. To define a zookeeper node, import the zookeeper module and set these variables:
$zookeeper_version– same as for hadoop, the version to deploy
$zookeeper_datastore– where to store the zookeeper data files
$zookeeper_datastore_log– where to store the zookeeper log
$zookeeper_myid– this needs to be configured for each individual node, as it assigns an unique id to the machine
The HBase deployment is very similar to the Hadoop one. You need to adjust the HBase configuration stored under modules/hbase/templates/conf/
$environment to add or remove any properties specific to your installation. In the configuration files you will spot some of the variables you have to set, like:
$hbase_version– what version to deploy; similar to the Hadoop case, this is part of the archive and folder name. If you use the default build script, it should pack it just right
$hbase_home– final directory to which the unpacked hbase will be symlinked to
$zookeeper_quorum– comma separated list of zookeeper nodes
$hbase_rootdir– HBase directory in HDFS, usualy
This was a quick run through some, but not all of the options that each recipe provides and requires. I strongly encourage you to go look in the provided nodes.pp which has a sample node configured with all of the options. Also, as a best practice, when adding your own properties to the template configuration files, you should try to use variables and set those on a per-node basis where applicable.
Using puppet to deploy the entire stack in an easy, predictable way has helped us a lot in not delaying cluster-wide upgrades just because it would be too hard to do. If you are deploying hstack on your custers, and decide to use these recipes, let us know if you find any bugs. If you’re using another way of pushing data and configuration to your cluster, we’d like to hear about it as well in the comments.