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UK Polling Stations build and deploy

Setup

  • pipenv install
  • ansible-galaxy install -r requirements.yml
  • Ensure your AWS credentials are in ~/.aws/credentials
  • cp packer-user-vars.example.json packer-user-vars.json and fill in the path to your private key file
  • create .vault_pass.txt with your vault password

Amazon Machine Images (AMI)

We use packer to build golden AMIS. On OSX this can be installed via brew install packer. The AMIs we build are designed to come up as quickly as possible so they can serve traffic. This means that they contain the entire AddressBase db pre-imported. To make import script-only or code-only changes quicker we have three AMIS:

  • The addressbase AMI which just has postgres with AddressBase imported
  • The imported-db AMI which is built off the addressbase AMI and also has the import scripts run against it.
  • The server AMI which is built off the imported-db AMI and also contains the code/app.

This makes the build process much faster if we want to deploy code-only updates. Each image is described as a builders object in packer.json.

How to build

If the there is a new AddressBase release or ONSUD release, or if you haven't built it yet then:

1. Fetch latest AddressBase and ONSUD

  • Order a new copy from the OS website and download it from their FTP
  • The files will be in a directory named something like DCS0000000000
  • Upload the files to s3://pollingstations-packer-assets/addressbase/DCS0000000000
  • Replace addressbase_folder_name in vars.yml with the directory name (e.g: DCS0000000000)
  • Replace onsud_url in vars.yml with the URL for the latest ONSUD release

2. Make the image

  • If you need to build the addressbase image run:

      AWS_PROFILE=democlub ./packer addressbase

    That will output an AMI id that you will need to manually copy. Look for lines like this near the end of the output:

    ==> database: Creating the AMI: addressbase 2016-06-20T12-38-27Z
    database: AMI: ami-7c8f160f

    (This might take a long time at the "Waiting for AMI to become ready..." stage)

    The AMI id (ami-7c8f160f in this case) needs to go into ./packer-vars.json in the database_ami_id key.

  • If the pollingstations/council dump has changed then similary to addressbase above run

      AWS_PROFILE=democlub ./packer imported-db

    and store the resulting AMI id in the imported-db_ami_id key in ./packer-vars.json.

    This will build one the addressbase AMI and include in the councils and polling stations data.

  • To make just a code change, build the server AMI. This is built on the imported-db AMI and just adds the code changes.

      AWS_PROFILE=democlub ./packer server

    NOTE: To run this you will need the Ansible Vault password. Place it in a .vault_pass.txt file in the same directory as this file. To view the vault variables run ansible-vault view vault.yml.

  • To deploy the image we've built:

    • Update aws.yml:

      • Set ami_id to image ID from last packer run (e.g: ami-2bbe8e4d)
      • Find the lc_num value of the previous instance we deployed and set lc_num to (previous lc_num + 1). This can be found by looking at the Launch Configuration names in the AWS console. When we deploy, this will clean up the previous image.
      • Set desired_capacity to a sensible number under "On-demand Autoscailing group" (e.g: 4 for peak times, 1 for off-peak). Note we use "On-demand Autoscailing group" for live/staging instances, "Spot price Autoscailing group" is used for building images so desired_capacity should be 1 for "Spot price Autoscailing group".

    • If we're deploying to production, export ENVIRONMENT=prod. Obviously don't do this if it is a staging deploy!

    • Run

      AWS_PROFILE=democlub ansible-playbook aws.yml -e replace_all=True

    This will create a new launch config, associated the ASG with it, and then delete the old one. If replace_all is set then it will also cycle all the old instances (1 by 1) to make them use new ones.

    • To test a staging deploy, ensure stage.wheredoivote.co.uk is pointed at the staging load balancer.
    • Once you've tested a staging build, the cleanest way to decommission the staging instance is to set the desired and minimum number of instances on the pollingstations-asg-test ASG to zero.

Debugging the build

If something is going wrong with the ansible or other commands you run on the build then the best tool for debugging it is to SSH onto the instance. By default packer will terminate the instance as soon as it errors though. If you add -debug (note: one dash) flag then packer will pause at each stage until you hit enter, giving you the time to SSH in and examine the server.

Packer will generate a per-build SSH private key which you will have to use:

ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no  \
  -l ubuntu -i ./ec2_server.pem 54.229.202.43

(The IP address will change every time too - get that from the output.)

Ad-hoc tasks

Sometimes you need to fix something urgently and you don't want to wait for an AMI rebuild. In which case you can use the ansible dynamic inventory:

ANSIBLE_HOST_KEY_CHECKING=False AWS_PROFILE=democlub \
ansible -i dynamic-inventory/ \
  -b --become-user polling_stations \
  tag_Env_prod \
  -a id

The above command will run id as the polling_stations user. This invokes the command module - you might want to add -a shell if your command is more complex.

What ever change you make don't forget to roll it back into the AMI, create a new launch config and update the ASG config (even if you don't replace the existing instances) otherwise a scaling event or failed host will "revert" your changes.

Ad-hoc deploy

ansible-playbook -u myusername -i dynamic-inventory/ -l tag_Env_prod deploy.yml --extra-vars @vault.yml

Take down data

ansible -u myusername -i dynamic-inventory/ -b --become-user polling_stations tag_Env_prod -m shell -a "cd /var/www/polling_stations/code/ && ../env/bin/python manage.py teardown -c X01000001"