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Upgrading Distributed Systems is not rsync

Upgrading Distributed Systems is not rsync. Sameer Ajmani Barbara Liskov Liuba Shrira MIT Lab for Computer Science. Large, Long-Lived Distributed Systems Need Automatic Upgrades. e.g., CDNs, peer-to-peer nets, sensor nets Software must change over time No direct operator access

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Upgrading Distributed Systems is not rsync

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  1. Upgrading Distributed Systemsis not rsync Sameer Ajmani Barbara Liskov Liuba Shrira MIT Lab for Computer Science

  2. Large, Long-Lived Distributed SystemsNeed Automatic Upgrades • e.g., CDNs, peer-to-peer nets, sensor nets • Software must change over time • No direct operator access • Upgrades must propagate automatically • Upgrades must avoid disrupting service

  3. A System Upgrade Version 1 Version 2 • Each node runs at a particular version • New version information propagates to nodes • A node upgrades by shutting down, installing new code, transforming its persistent state, and restarting • These systems are robust, so they tolerate node restarts

  4. Upgrades Can Disrupt Service Version 1 Version 2 • A node cannot service requests while upgrading • May need to delay a node upgrade • To avoid causing too many simultaneous failures • To test an upgrade on a few nodes • Implies mixed mode operation

  5. Mixed Mode Operation Version 2 Version 1

  6. Simulation Enables Interoperation Version 1 Node Version 2 • Nodes label outgoing calls with their version • Nodes dispatch incoming calls to simulation objects • Installing a simulation object is much faster than upgrading • Both upgraded and non-upgraded nodes use simulation • Imperfect simulation may degrade service

  7. Summary • Upgrades require scheduling and simulation • Other issues (covered in the paper) • Transforms for persistent state • Correctness of transforms and simulation • An upgrade infrastructure that supports upgrade propagation, scheduling, code installation, transforms, and simulation

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