sahara/doc/source/overview.rst

Rationale

Introduction

Apache Hadoop is an industry standard and widely adopted MapReduce implementation, it is one among a growing number of data processing frameworks. The aim of this project is to enable users to easily provision and manage clusters with Hadoop and other data processing frameworks on OpenStack. It is worth mentioning that Amazon has provided Hadoop for several years as Amazon Elastic MapReduce (EMR) service.

Sahara aims to provide users with a simple means to provision Hadoop, Spark, and Storm clusters by specifying several parameters such as the version, cluster topology, hardware node details and more. After a user fills in all the parameters, sahara deploys the cluster in a few minutes. Also sahara provides means to scale an already provisioned cluster by adding or removing worker nodes on demand.

The solution will address the following use cases:

• fast provisioning of data processing clusters on OpenStack for development and quality assurance(QA).
• utilization of unused compute power from a general purpose OpenStack IaaS cloud.
• "Analytics as a Service" for ad-hoc or bursty analytic workloads (similar to AWS EMR).

Key features are:

• designed as an OpenStack component.

• managed through a REST API with a user interface(UI) available as part of OpenStack Dashboard.

• support for a variety of data processing frameworks:

  • multiple Hadoop vendor distributions.
  • Apache Spark and Storm.
  • pluggable system of Hadoop installation engines.
  • integration with vendor specific management tools, such as Apache Ambari and Cloudera Management Console.

• predefined configuration templates with the ability to modify parameters.

Details

The sahara product communicates with the following OpenStack services:

• Dashboard (horizon) - provides a GUI with ability to use all of sahara’s features.
• Identity (keystone) - authenticates users and provides security tokens that are used to work with OpenStack, limiting a user's abilities in sahara to their OpenStack privileges.
• Compute (nova) - used to provision VMs for data processing clusters.
• Orchestration (heat) - used to provision and orchestrate the deployment of data processing clusters.
• Image (glance) - stores VM images, each image containing an operating system and a pre-installed data processing distribution or framework.
• Object Storage (swift) - can be used as storage for job binaries and data that will be processed or created by framework jobs.
• Block Storage (cinder) - can be used to provision block storage for VM instances.
• Networking (neutron) - provides networking services to data processing clusters.
• Telemetry (ceilometer) - used to collect measures of cluster usage for metering and monitoring purposes.
• Shared file systems (manila) - can be used for storage of framework job binaries and data that will be processed or created by jobs.

General Workflow

Sahara will provide two levels of abstraction for the API and UI based on the addressed use cases: cluster provisioning and analytics as a service.

For fast cluster provisioning a generic workflow will be as following:

• select a Hadoop (or framework) version.

• select a base image with or without pre-installed data processing framework:

  • for base images without a pre-installed framework, sahara will support pluggable deployment engines that integrate with vendor tooling.
  • you can download prepared up-to-date images from http://sahara-files.mirantis.com/images/upstream/liberty/

• define cluster configuration, including cluster size, topology, and framework parameters (for example, heap size):

  • to ease the configuration of such parameters, configurable templates are provided.

• provision the cluster; sahara will provision VMs, install and configure the data processing framework.

• perform operations on the cluster; add or remove nodes.

• terminate the cluster when it is no longer needed.

For analytics as a service, a generic workflow will be as following:

• select one of the predefined data processing framework versions.

• configure a job:

  • choose the type of job: pig, hive, jar-file, etc.
  • provide the job script source or jar location.
  • select input and output data location.

• set the limit for the cluster size.

• execute the job:

  • all cluster provisioning and job execution will happen transparently to the user.
  • cluster will be removed automatically after job completion.

• get the results of computations (for example, from swift).

User's Perspective

While provisioning clusters through sahara, the user operates on three types of entities: Node Group Templates, Cluster Templates and Clusters.

A Node Group Template describes a group of nodes within cluster. It contains a list of hadoop processes that will be launched on each instance in a group. Also a Node Group Template may provide node scoped configurations for those processes. This kind of template encapsulates hardware parameters (flavor) for the node VM and configuration for data processing framework processes running on the node.

A Cluster Template is designed to bring Node Group Templates together to form a Cluster. A Cluster Template defines what Node Groups will be included and how many instances will be created in each. Some data processing framework configurations can not be applied to a single node, but to a whole Cluster. A user can specify these kinds of configurations in a Cluster Template. Sahara enables users to specify which processes should be added to an anti-affinity group within a Cluster Template. If a process is included into an anti-affinity group, it means that VMs where this process is going to be launched should be scheduled to different hardware hosts.

The Cluster entity represents a collection of VM instances that all have the same data processing framework installed. It is mainly characterized by a VM image with a pre-installed framework which will be used for cluster deployment. Users may choose one of the pre-configured Cluster Templates to start a Cluster. To get access to VMs after a Cluster has started, the user should specify a keypair.

Sahara provides several constraints on cluster framework topology. JobTracker and NameNode processes could be run either on a single VM or two separate VMs. Also a cluster could contain worker nodes of different types. Worker nodes could run both TaskTracker and DataNode, or either of these processes alone. Sahara allows a user to create a cluster with any combination of these options, but it will not allow the creation of a non-working topology (for example: a set of workers with DataNodes, but without a NameNode).

Each Cluster belongs to an Identity service project determined by the user. Users have access only to objects located in projects they have access to. Users can edit and delete only objects they have created or exist in their projects. Naturally, admin users have full access to every object. In this manner, sahara complies with general OpenStack access policy.

Integration with Object Storage

The swift project provides the standard Object Storage service for OpenStack environments; it is an analog of the Amazon S3 service. As a rule it is deployed on bare metal machines. It is natural to expect data processing on OpenStack to access data stored there. Sahara provides this option with a file system implementation for swift HADOOP-8545 and Change I6b1ba25b which implements the ability to list endpoints for an object, account or container. This makes it possible to integrate swift with software that relies on data locality information to avoid network overhead.

To get more information on how to enable swift support see userdoc/hadoop-swift.

Pluggable Deployment and Monitoring

In addition to the monitoring capabilities provided by vendor-specific Hadoop management tooling, sahara provides pluggable integration with external monitoring systems such as Nagios or Zabbix.

Both deployment and monitoring tools can be installed on standalone VMs, thus allowing a single instance to manage and monitor several clusters at once.