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Goals

  • CDAP and CDAP Applications have the ability to withstand short and transient infrastructural outages
  • During interruption of underlying services (one or more), CDAP or CDAP Applications can operate under degraded performance/limited functionalities 
    • Users will not be able to perform operations like deploying apps, starting programs or new data or application lifecycle operations.
      • However all the applications that are running, should be running
  • Once interruption in the underlying service is resolved or services come back to normal operation, the CDAP and CDAP Application will go back to normal state 
  • Interruptions in service would be due to node failure, service failures or compatible rolling upgrades or downgrades in progress
  • Does not include in-compatible upgrades or downgrades of underlying infrastructure 
  • Does not include long unavailability of service and infrastructure

Area of Focus

  • CDAP system resiliency to infrastructure unavailability or interruption for long periods of time
  • CDAP Rolling Upgrades
  • CDAP Application Rolling Upgrades

High Level Requirements

  • Compatible Upgrade or Downgrade of underlying infrastructure Hadoop components
    • Underlying Hadoop infrastructure is either being upgraded or downgraded and the expectation is that CDAP and CDAP Applications should tolerate and be resilient to infrastructure services not being available during the upgrade or downgrade process. 
    • The upgrade or downgrade process could take anywhere between 30 mins - 18 hours or more. 
    • During the period of service unavailability or interruption, the CDAP and CDAP Applications operate in degraded mode.
    • Hadoop infrastructure upgrade / downgrade has to be compatible with CDAP and CDAP Application in order to have smooth upgrades
    • In case, there are issues during the upgrade, CDAP should be resilient to rollbacks
    • CDAP and CDAP Applications should also be able to withstand compatible downgrades
    • The compatibility matrix should be available to users to ensure smooth upgrades
  • Upgrade / Downgrade of CDAP
    • Upgrade a CDAP version. Major and minor version could have different impacts. We will discuss about these impact further in the document. 
    • Roll back of CDAP upgrade or downgrade
    • CDAP version compatible matrix available to users
    • Dry run for upgrade and downgrade
  • Upgrade / Downgrade of CDAP Applications
    • Upgrade or Downgrade a CDAP Application

    • Rolling upgrade of live services like CDAP Services, Flow and Spark Streaming

Technical Breakdown

RS-001 : Un-interrupted update of compact modules in co-processor

CDAP system uses few HBase coprocessors to optimize the operations being performed on HBase. When underlying HBase is upgraded, the table has to be altered. This means that the table has to be disabled. Disabling the table can have multiple side effects on CDAP, so the recommended approach right now is to stop applications running within CDAP as well as CDAP. For each version of non-compatible HBase, CDAP has a compat module has to updated.

RS-002 : Client resiliency

CDAP as a system or CDAP Applications through CDAP APIs directly or in-directly connect with Kafka, HBase, HDFS, YARN, Zookeeper as well as other CDAP systems. All client APIs currently have a pre-defined timeout before they fail. This behavior is not suitable for handle failures in underlying system. The clients should exhibit back-off behavior in case of failures resulting in degraded behavior. Once the issue is resolved then client should immediately get back to normal operation. 

RS-003 : Move Dataset management out of CDAP Master

Dataset service currently resides within CDAP Master. All Dataset initialization would require to contact Dataset Service within CDAP Master to load dataset artifacts. In case of unavailability of CDAP Master the dataset initialization would fail and that would cause clients to fail, in turn would fail the programs performing the dataset operation. Moving Dataset Service out of CDAP Master and moving Dataset libraries into standard artifact infrastructure would allow to reduce this dependency.  

RS-004 : CDAP version definition and guarantees of version

CDAP version would have to provide strong guarantees. Things like change in major version might not support rolling upgrade, patch upgrades should be able to jump to any patch within minor version, Minor version upgrades. Handing of API deprecation, Beta and GA. Beta API contracts, would they affect rolling upgrade. What version component guarantee binary compatibility, source compatibility, wireformat compatibility. When does CDAP app need to be rebuilt. If they have to rebuilt, how the application should be upgraded. 

RS-005 : Internal schema evolution and management

Most network endpoint are versioned, but they are not complete. All the internal schemas should versioned (schema hash concept) and support for compatible schema changes. 

RS-006 : Managing infrastructure incompatibility 

When underlying upgrade or downgrade creates incompatibility, the CDAP system and CDAP Applications should be able to handle transient incompatibilities service disruptions. This might be prevented with documentation and publishing of compatibility matrix, but the system still should be able to handle the impact. 

RS-007 : System state transition and management 

During the rolling upgrade process the system has to be transitioned from one state to the other. Different sub-systems could in different states and those need to be managed. This is also applicable not only to CDAP System, but also to CDAP Applications.  

RS-008 : Apache Twill Application rolling upgrade 

In order to support rolling upgrade of CDAP Applications, capability needs to be added to Apache Twill Application. 

RS-009 : Upgrade orchestrator

The whole upgrade process has to be co-ordinated across multiple sub-systems for CDAP system and components for CDAP Application. The orchestrator is responsible for managing the lifecycle of rolling upgrade, reporting the status of upgrade. 

RS-010 : Progressive background upgrade tool 

Rolling upgrade at times would involve transitioning data, metadata from one format to another, if this process has to be non-intrusive, then it should be implemented as progressive process.

RS-011 : Hydrator pipeline upgrade 

Hydrator pipelines are currently not compatible across major, minor or bug fix release as they are tightly tied to the exact version. This should follow the same or similar guidelines RS-004. 

RS-012 : Dataset upgrade 

In some cases there might system dataset used by the CDAP system or user datasets that are part of CDAP Applications that need to be migrated during the upgrade process, so the system should be support upgrading both types of datasets as part of RS-010.

RS-013 : Test framework and chaos monkey

From platform perspective, there should exists a solid end-2-end testing framework for testing known scenarios, but a chaos monkey would provide a more comprehensive testing. 

RS-014 : User Interface / REST APIs / CLI

There should exist the ability to initiate, manage, monitor and track the progress of rolling upgrades / downgrades. These are accessible through CDAP User Interface, REST API and Command Line Interface. 

RS-015 : Support for rollbacks

In case of failure to upgrade or downgrade mid through the process, the RS-009 should have the ability to rollback and restore the state of the system to point before the start of the process. 

Open Item/Discussion point

  • Define long and short/transient outages
    • More information to gathered here to understand the length of outages. 
    • When outages are multiple hours, how should the system handle these. 

Action Items

  • Oct 7th 2016

    • (tick) Send supported HBase version by CDAP
    • Gather information about CDH version compatibility changes – Talk to Cloudera and compile 

 

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