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ansible-puller

This daemon extends the ansible-pull method of running Ansible. It uses S3 or HTTP file transmission instead of Git to manage distribution (easy to cache), and integrates with Prometheus monitoring.

Why ansible-puller?

ansible-pull assumes that you are checking out an Ansible repository from git. This wasn't an option for us at the scale that we needed, so we turned to HTTP file distribution. On top of scaling, we've integrated monitoring (via Prometheus) to retain the centralized view of all of our Ansible runs and a simple REST API to enable/disable the puller and trigger a run to give more fine-grained control of rollouts.

How to use it

Ansible puller expects an HTTP endpoint, or an S3 ARN that points to a tarball with Ansible playbooks, inventories, etc.

The minimal configuration would just be a config file supplying http-url (see below). While the defaults have been set assuming Ansible's "Alternative Directory Layout" it should be configurable enough to support alternative setups.

Inside of the tarball, at a minimum you'll need an inventory, playbook, and a requirements.txt file. The requirements file will be used to populate the Python virtual environment that Ansible will run in locally. At a minimum it needs to contain ansible so that Ansible will be installed in the virtualenv. A pinned version is even better. The playbook is what will be actually run. The inventory needs to contain the hostname of the node that Ansible puller is installed on.

Ansible Inventory

To support our use of an Infrastructure monorepo, Ansible-puller will loop through an entire directory looking for inventories. It will test each of these inventories for a matching hostname and run the given playbook in the first found inventory.

Given the structure:

.
├── ansible.cfg
├── inventories/
│   ├── production/
│   └── staging/
├── roles/
└── site.yml

And the config file:

{
  "http-url": "https://example.com/infra.tgz",
  "ansible-inventory": ["inventories/production", "inventories/staging"],
  "playbook": "site.yml"
}

Setting ansible-inventory to ["inventories/production", "inventories/staging"] and playbook to site.yml would mean that the puller would search for the correct host in production and staging, provided that the hosts were a part of site.yml's run. Use the debug option to get more insight to the process while it is running.

Configuration and Metrics

Config file should be in: /etc/ansible-puller/config.json, $HOME/.ansible-puller.json, ./ansible-puller.json

Config Option Default Description
http-listen-string "0.0.0.0:31836" Address/port the service will listen on. Use 127.0.0.1:31386 to lock down the UI.
http-proto https Modify to "http" if necessary
http-user "" Username for HTTP Basic Auth
http-pass "" Password for HTTP basic Auth
http-url "" HTTP Url to find the Ansible tarball. Required if s3-arn is not set
http-checksum-url "" HTTP Url to find the Ansible tarball md5 hash. Defaults to http-url + .md5.
log-dir "/var/log/ansible-puller" Log directory (must exist)
ansible-dir "" Path in the pulled tarball to cd into before ansible commands - usually ansible.cfg dir
ansible-playbook "site.yml" The playbook that will be run - relative to ansible-dir
ansible-inventory [] List of inventories to operate on - relative to ansible-dir
venv-python "/usr/bin/python3" Path to the python version you are using for Ansible
venv-path "/root/.virtualenvs/ansible_puller" Path to where the virtualenv will be created
venv-requirements-file "requirements.txt" Path to the python requirements file to populate the virtual environment
sleep 30 How often to trigger run events in minutes
start-disabled false Whether or not to start with Ansbile disabled (good for debugging)
s3-arn "" S3 location to find the Ansible tarball. Required if http-url is not set
s3-conn-region "" S3 connection region to use. Uses the aws-sdk-go-v2 default providers if not set
debug false Whether or not to start in debug mode
once false Only run the configured playbook once and then stop

Monitoring with prometheus

This daemon uses Ansible's json STDOUT callback to parse the results of this run for this host. It currently produces the number of tasks that are ok, skipped, changed, failed, or unreachable.

Metric Description
ansible_puller_debug Whether or not debug mode is enabled
ansible_puller_disabled Whether or not the puller is disabled
ansible_puller_last_success Last timestamp of a successful run
ansible_puller_last_exit_code Last ansible run exit code
ansible_puller_play_summary Ansible metrics: changed, failures, ok, skipped, unreachable
ansible_puller_run_time_seconds How long Ansible took to run to completion
ansible_puller_running Whether or not the puller is currently running
ansible_puller_runs How many times the puller has run
ansible_puller_version Version (git sha) of the puller

MD5 checksum support

Enabling MD5 checksumming will prevent extraneous calls to download the ansible tarball from the remote.

By design, ansible_puller will look at the remote path <resource_path>.md5 to discover the live MD5 checksum. If, for example, your resource is located at https://example.com/some/file.tgz then ansible_puller will look for the MD5 hash at https://example.com/some/file.tgz.md5. A custom remote path can be specified with the http-checksum-url option. The following conditions will lead to a (re-)download of the ansible tarball:

  • There is no current ansible tarball at the specified local path
  • The current hash of the local ansible tarball not match the remote checksum
  • The remote checksum does not exist

If a remote checksum exists then the downloaded tarball will be hashed and the resulting output will be compared to the remote checksum to validate artifact integrity.

Runtime Dependencies

This program expects the following to be true about its runtime environment:

  • It is running as root (unless you don't need --become)
  • virtualenv is installed on the server

Development Notes

This project uses Go Modules. Go 1.19+ should be able to handle this transparently.

Doing Things

Running Locally

bazelisk run //:ansible_puller

or, without bazel

go run .

Running tests

bazelisk test //...

Building a Production Release

bazelisk build --config=release --platforms=@io_bazel_rules_go//go/toolchain:linux_amd64 //...

Building Production Packages

  • bazelisk build --config=release //:ansible_puller_deb
  • bazelisk build --config=release //:ansible_puller_rpm

Debugging an Ansible Run

For debugging the application, use the --debug flag, or the debug option in the config file. This streams the Ansible output to the console so that you can follow along in the run.

Also consider using the --once flag to run the process just once and then exit without spinning up the webserver.