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Alexis Wilke
Asked: 2014-03-01 16:42:30 +0800 CST

Upgrading your cloud application when running it on a live cluster?

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I am working on a cloud based application which installed under Ubuntu as you would otherwise expected. For example, the server is installed as follow:

apt-get install snapserver

We have nearly 20 packages as part of the project now.

We do not yet have a running cluster, but are thinking that at some point we'd have many computers running with the software, some computers as frontends, and some computers as backends.

My question is: how do you usually update a live cluster? My concern is that new code may generate new entries in the database that are not compatible with the old code. If that happens and a client access a server that still runs the old version, it could end up crashing.

What is the best practice in this case?

linux

1 Answers

  1. A sort of transactional deployment process would work here. Essentially what you would do is:

    • spin up a second cluster
    • copy current production data to a new database server (ensure you keep this DB updated with current data)
    • spin up second application processes
    • run system tests
      • if system tests pass, kill old cluster
      • if system tests fail, back to dev, shut down newly setup cluster

    It's easier to do something like this when you have a VM container provider like VMware, AWS, Heroku, OpenStack, etc.

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