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Comment: Changed cases of headings, and wordings in "Testing"

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BD-703. To add Docker containers as a new granularity in the VM elasticity module, thus expands its functionality.

  • Design

    questions

    Questions and

    answers

    Answers

  1. Should an extractor type be managed by both an VM image and docker, or only one of them?
    A: only one for simplicity. So need to specify this piece of information in the config file.
  2. Support managing the extractors both using VM images and using Docker containers at the same time?
    A: Yes.

  3. Separate docker machines than the other machines? Or on the same machines?

    A: Separate. 

  4. Docker image storage: docker hub, or a private registry?
    A: Docker hub for now. Setting up a private registry takes time and a secure one requires getting a certificate from a CA. Can do it later when needed. Use ncsa/clowder-ocr, ncsa/clowder-python-base, ncsa/clowder-opencv-closeups, etc. for now. Done.

  5. How do we restart a docker container if the application crashed/stopped?
    A: docker run --restart=always ...
    This will retry indefinitely, but with a delay that doubles before each retry, starting from 100 ms (0.1 second), to avoid flooding the server. Can also consider using "--restart=on-failure[:max-retries]" to limit the number of retries, but then that could leave a container in the stopped state, without any component to restart it. Usually a RabbitMQ server restart would cause an error, and the error was observed to persist for about 2 minutes.
  6. How do we scale up an application managed by docker?
    A: see below.
  7. How do we scale down?
    A: see below.
    1. Do we suspend and resume docker VMs, or always keep them running?
      A: We suspend and resume docker VMs, but keep at least 1.
  8. A manually created and updated VM image is used to start "Docker machines" or "Docker VMs" to host the docker containers. How do we start the Docker machines – externally bootstrap, or start them using the elasticity module?
    A: Use the elasticity module. Add the docker VM image info in the config file, set a min # of 1. Later on the scaling-up logic will start more as needed. Need special handling: the dockerized extractors depend on its existence, so if not already existing, a Docker machine needs to be started first.
  9. How do we detect idle extractors managed by docker?
    A: Same logic using the RabbitMQ API as before. After detection, perform docker-specific commands to stop the idle extractors.
  10. How do we detect idle docker machines if no container runs on them?
    A: Since a Docker machine itself does not make RabbitMQ connections.If no extractor runs on it, it won't show up in the extr->VM or VM->extr maps, so need to maintain separate maps for the Docker machines. Find the Docker machines that have no extractors running on them, add them to the idle VM list.
  11. How do we specify mapping of docker images with extractors?
    A: add a [Docker] section in the config file, 1 to 1 mapping: "extr1: dockerimg1". When starting the elasticity module, load the config file, and check for errors: one extractor type should be managed only by one method: either docker or a VM image. If such configuration errors exist, print out, and use a default type such as docker – also make this choice a configurable item in the config file.
  12. Details of the Docker VM image?
    A: Ubuntu 14.04 base image + Docker installed.
    In the config file [OpenStack Image Info] section:
         docker-ubuntu-trusty = docker, m1.large, ubuntu, NCSA-Nebula, ''
    Use a larger flavor (4 or 8 CPUs), since one docker VM hosts multiple containers. Pull all needed docker images for the extractors for faster container start time at run time. Nice to have: ensure that the docker images specified are valid and available, pull them if not already – when starting the module.

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  • Programming Language and Application Type

Continue with the existing use of Python and a stand-alone program.

  • Testing

  • Input
    Use a script to generate high request rates with OCR , and OpenCV extractors to test the scaling up part. Stop sending the requests to test the scaling down part.
  • Output
    Use the OpenStack CLI / web UI for to monitor the VM partVMs, and use the RabbitMQ web UI and SSH ssh into the docker machines for to monitor the extractor partextractors, to verify that the docker containers are started/stopped, and the docker VMs are started/resumed/suspended as expected.

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