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

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Technical Breakdown

RS-001 : Un-interrupt update of compact modules in Coprocessor

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.

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