Ansible Role: ansible-bluegreen-docker

Simple Ansible role showing the concept of downtimeless deployments with Docker containers, but without orchestrator (Swarm, Kubernetes, etc.)

Disclaimer

Yes, I know about Kubernetes/Nomad/Swarm and other better methods to deploy an application in Docker containers. But there are cases, where the usage of orchestrator is bringing excessive complexity and is ""heavier" than an actual application workload.

If your infrastructure has one or two hosts and you need to deploy containerized web applications to them effectively, this role might be helpful.

The original pattern of blue-green deployments describes two copies of entire infrastructure with a router, switching traffic from old copy to a new one after a successful deployment.

This pattern can not be applied in this role to the full extent. However, during the run, the role will create a set of new containers alongside the old ones still running. The traffic will be switched to new containers (by modifying Nginx config) only after a successful healthcheck. So as you can see, the approach is quite similar to the original blue-green idea.

The deployment itself is done by docker_container Ansible module. Please refer to its documentation for more details.

Role Variables

Variable	Description	Default
app_name	Application name. Also used for container naming.	trainingwheels
app_image	Name of the Docker image to pull.	decayofmind/trainingwheels
app_port	Internal TCP port where app is listening for connections.	5000
app_version	Docker image tag.	latest
app_instances_count	Number of containers to be run.	2
app_command	Command to be executed in a container	""
app_etc_hosts	Custom hostname to IP mappings for /etc/hosts in container.	{}
app_env	Environment variables passed to a container's shell.	{}
app_volumes	Volumes mounted into container.	[]
app_log_driver	Driver for capturing logs in containers.	none
app_log_options	Options for log driver.	{}
app_port_prefix	Prefix for ports, opened for containers on host if app_bluegreen_enabled is disabled.	401
app_bluegreen_enabled	Enables downtimeless deployment.	yes
app_bluegreen_default_color	Tag for the first deployment (better to leave as is).	green
app_bluegreen_tags.blue	Hash with defaults for blue deployments (better to leave as is).	{"name":"blue", "port_prefix": 402}
app_bluegreen_tags.green	Hash with defaults for green deployments (better to leave as is).	{"name":"green", "port_prefix": 407}
app_nginx_enabled	Enables generation of Nginx config for balancing between containers.	yes
app_nginx_hostnames	Hostanames, which Nginx will accept.	["localhost"]
app_nginx_upstream_name	Upstream name for Nginx configuration (better to leave as is).	{{ app_name }}
app_nginx_port	Port where Nginx is listening to incoming external requests.	80
app_nginx_ip_hash	Enable ip-hash load-balancing algorithm for nginx.	no
app_nginx_crossbalance_enabled	Application containers of other hosts will be added to Nginx upstream if enabled.	yes
app_nginx_crossbalance_hosts	List of hosts to add to Nginx upstream (better to leave as is).	{{ ansible_play_hosts }}
app_nginx_conf_backup_retention	Count of Nginx configuration backup to keep	3
app_old_containers_treatment_enabled	Enable to stop or remove containers left from the previous deployment.	yes
app_old_containers_treatment_type	What to do with containers of previous deployment (color). May be absent or stopped.	absent
app_healthcheck_enabled	Perform a healthcheck on newly deployed containers.	yes
app_healthcheck_path	Healthcheck path.	/
app_cleanup_dead_containers	Enables deletion of any dead containers left.	yes

Temporary Variables

Following variables will appear in runtime:

Variable	Description
_app_first_run	Is True if role is run for the first time (local facts are checked for it).
_app_prev_color	Tag of the previous deployment (fetched from local facts of app_default_color).
_app_prev_count	Containers count of the previous deployment (fetched from local facts).
_app_prev_version	Previous version of the deployed application (fetched from local facts).
_app_next_color	Tag of the ongoing deployment. The opposite of _app_prev_color.
_app_deployemnt	Returned values from docker_container module.
_app_ports	Exposed ports of newly deployed containers (taken from _app_deployment).
_app_dead_containers	Hashes of containers with dead status if found.
_app_healthcheck_result	Result of ongoing healthchecks.
_app_nginx_conf_test	Result of Nginx config check.

Requirements

• docker-engine (not in meta)
• nginx (not in meta)

Additionally for my test application (decayofmind/trainingwheels) you will need Redis.

Nginx Balancing

1. Ansible gets a list of all published ports in containers.
2. Ansible prepares an Nginx config with all published container's ports of all(!) app hosts.

Desired Architecture