Tuesday, November 11, 2014

Genie 2.0: Second Wish Granted!

By Tom Gianos and Amit Sharma @ Big Data Platform Team

A little over a year ago we announced Genie, a distributed job and resource management tool. Since then, Genie has operated in production at Netflix, servicing tens of thousands of ETL and analytics jobs daily. There were two main goals in the original design of Genie:

  • To abstract execution environment from the Hadoop, Hive and Pig job submissions.
  • To enable horizontal scaling of client resources based on demand.

Since the development of Genie 1.0, much has changed in both the big data ecosystem and here at Netflix. Hadoop 2 was officially released, enabling clusters to use execution engines beyond traditional MapReduce. Newer tools, such as interactive query engines like Presto and Spark, are quickly gaining in popularity. Other emerging technologies like Mesos and Docker are changing how applications are managed and deployed. Some changes to our big data platform in the last year include:

  • Upgrading our Hadoop clusters to Hadoop 2.
  • Moving to Parquet as the primary storage format for our data warehouse.
  • Integrating Presto into our big data platform.
  • Developing, deploying and open sourcing Inviso, to help users and admins gain insights into job and cluster performance.

Amidst all this change, we reevaluated Genie to determine what was needed to meet our evolving needs. Genie 2.0 is the result of this work and it provides a more flexible, extensible and feature rich distributed configuration and job execution engine.

Reevaluating Genie 1.0

Genie 1.0 accomplished its original goals well, but the narrow scope of those goals lead to limitations including:

  • It only worked with Hadoop 1.
  • It had a fixed data model designed for a very specific use case. Code changes were required to accomplish minor changes in behavior.
    • As an example, the s3CoreSiteXml, s3HdfsSiteXml fields of the ClusterConfigElement entity stored the paths to the core-site and hdfs-site XML files of a Hadoop cluster rather than storing them as a generic collection field.
  • The execution environment selection criteria was very limited. The only way to select a cluster was by setting one of three types of schedules: SLA, ad hoc or bonus.

Genie 1.0 could not continue to meet our needs as the number of desired use cases increased and we continued to adopt new technologies. Therefore, we decided to take this opportunity to redesign Genie.

Designing and Developing Genie 2.0

The goals for Genie 2.0 were relatively straightforward:

  • Develop a generic data model, which would let jobs run on any multi-tenant distributed processing cluster.
  • Implement a flexible cluster and command selection algorithm for running a job.
  • Provide richer API support.
  • Implement a more flexible, extensible and robust codebase.

Each of these goals are explored below.

The Data Model

The new data model consists of the following entities:

Cluster: It stores all the details of an execution cluster including connection information, properties, etc. Some cluster examples are Hadoop 2, Spark, Presto, etc. Every cluster can be linked to a set of commands that it can run.

Command: It encapsulates the configuration details of an executable that is invoked by Genie to submit jobs to the clusters. This includes the path to the executable, the environment variables, configuration files, etc. Some examples are Hive, Pig, Presto and Sqoop. If the executable is already installed on the Genie node, configuring a command is all that is required. If the executable isn’t installed, a command can be linked to an application in order to install it at runtime.

Application: It provides all the components required to install a command executable on Genie instances at runtime. This includes the location of the jars and binaries, additional configuration files, an environment setup file, etc. Internally we have our Presto client binary configured as an application. A more thorough explanation is provided in the “Our Current Deployment” section below.

Job: It contains all the details of a job request and execution including any command line arguments. Based on the request parameters, a cluster and command combination is selected for execution. Job requests can also supply necessary files to Genie either as attachments or via the file dependencies field, if they already exist in an accessible file system. As a job executes, its details are recorded in the job record.

All the above entities support a set of tags that can provide additional metadata. The tags are used for cluster and command resolution as described in the next section.

Job Execution Environment Selection

Genie now supports a highly flexible method to select the cluster to run a job on and the command to execute, collectively known as the execution environment. A job request specifies two sets of tags to Genie:

  • Command Tags: A set of tags that maps to zero or more commands.
  • Cluster Tags: A priority ordered list of sets of tags that maps to zero or more clusters.

Genie iterates through the cluster tags list, and attempts to use each set of tags in combination with the command tags to find a viable execution environment. The ordered list allows clients to specify fallback options for cluster selection if a given cluster is not available.

At Netflix, nightly ETL jobs leverage this feature. Two sets of cluster tags are specified for these jobs. The first set matches our bonus clusters, which are spun up every night to help with our ETL load. These clusters use some of our excess, pre-reserved capacity available during lower traffic hours for Netflix. The other set of tags match the production cluster and act as the fallback option. If the bonus clusters are out of service when the ETL jobs are submitted, the jobs are routed to the main production cluster by Genie.

Richer API Support

Genie 1.0 exposes a limited set of REST APIs. Any updates to the contents of the resources had to be done by sending requests, containing the entire object, to the Genie service. In contrast, Genie 2.0 supports fine grained APIs, including the ability to directly manipulate the collections that are part of the entities. For a complete list of available APIs, please see the Genie API documentation.

Code Enhancements

An examination of the Genie 1.0 codebase revealed aspects that needed to be modified in order to provide the flexibility and standards compliance desired going forward.
Some of the goals to improve the Genie codebase were to:

  • Decouple the layers of the application to follow a more traditional three tiered model.
  • Remove unnecessary boilerplate code.
  • Standardize and extend REST APIs.
  • Improve deployment flexibility.
  • Improve test coverage.

Tools such as Spring, JPA 2.0, Jersey, JUnit, Mockito, Swagger, etc. were leveraged to solve most of the known issues and better position the software to handle new ones in the future.

Genie 2.0 was completely rewritten to take advantage of these frameworks and tools. Spring features such as dependency injection, JPA support, transactions, profiles and more are utilized to produce a more dynamic and robust architecture. In particular, dependency injection for various components allows Genie to be more easily modified and deployed both inside and outside Netflix. Swagger based annotations on top of the REST APIs provide not only improved documentation, but also a mechanism for generating clients in various languages. We used Swagger codegen to generate the core of our Python client, which has been uploaded to Pypi. Almost six hundred tests have also been added to the Genie code base, making the code more reliable and maintainable.

Our Current Deployment
Genie 2.0 has been deployed at Netflix for a couple of months, and all Genie 1.0 jobs have been migrated over. Genie currently provides access to all the Hadoop and Presto clusters, in our production, test and ad hoc environments. In production, Genie currently autoscales between twelve to twenty i2.2xlarge AWS instances, allowing several hundred jobs to run at any given time. This provides horizontal scaling of clients for our clusters with no additional configuration or overhead.

Presto and Sqoop commands are each configured with a corresponding application that points to locations in S3, where all the jars and binaries necessary to execute these commands are located. Every time one of these commands run, the necessary files are downloaded and installed. This allows us to continuously deploy updates to our Presto and Sqoop clients without redeploying Genie. We’re planning to move our other commands, like Pig and Hive, to this pattern as well.

At Netflix launching a new cluster is done via a configuration based launch script. After a cluster is up in AWS, the cluster configuration is registered with Genie. Commands are then linked to the cluster based on predefined configurations. After it is properly configured in Genie, the cluster will be marked as “available”. When we need to take down a cluster, it is marked as “out of service” in Genie so the cluster can no longer accept new jobs. Once all running jobs are complete, the cluster is marked as “terminated” in Genie and instances are shut down in AWS.

With Genie 2.0 going live in our environment, it has allowed us to bring together all the new tools and services we’ve added to the big data platform over the last year. We have already seen many benefits from Genie 2.0. We were able to add Presto support to Genie in a few days and Sqoop in less than an hour. Theses changes would have required code modification and redeployment with Genie 1.0, but were merely configuration changes in Genie 2.0.
Below is our new big data platform architecture with Genie at its core.


Future Work

There is always more to be done. Some enhancements that can be made going forward

  • Improving the job execution and monitoring components for better fault tolerance, efficiency on hosts and more granular status feedback.
  • Abstracting Genie’s use of Netflix OSS components to allow adopters to implement their own functionality for certain components to ease adoption.
  • Improving the admin UI to expose more data to users. e.g. Show all clusters a given command is registered with.

We’re always looking for feedback and input from the community on how to improve and evolve Genie. If you have questions or want to share your experience with running Genie in your environment, you can join our discussion forum. If you’re interested in helping out, you can visit our Github page to fork the project or request features.