gantryd

A framework built on top of Docker that allows for easy deployment and management of project components, with a focus on:

• Easy management of components of a project across multiple machines
• Single command updating of components with automatic draining and progressive rollout
• Ability to manage components locally, when necessary (see gantry below)

Overview

gantryd is a distributed, etcd-based system for running, updating, monitoring and managing various Docker images (known as "components") across multiple machines.

gantryd manages the running, monitoring and draining of containers, automatically updating machines progressively on update, and draining the old containers as it goes along. A container is only shutdown when all connections to it have terminated (or it is manually killed). This, combined with progressive update, allows for continuous deployment by simply pushing a new docker image to a repository and running update via gantryd.py.

gantryd also automatically monitors the containers of a component, running checks periodically to ensure they are healthy. If a container goes bad, a new one is automatically started in its place, with traffic being moved over.

Getting Started

Getting etcd

The latest etcd release is available as a binary at Github. Installation instructions can be found at Etcd README.

Cloning the source

git clone https://github.com/DevTable/gantryd.git

Installing dependencies

# Install apt-get dependencies.
cat requirements.system | xargs sudo apt-get install -y

# Install python dependencies.
sudo pip install -r requirements.txt

Setting up

All settings for gantryd are defined in a JSON format. A project's configuration is stored in etcd but is set initially from a local file (see setconfig below).

The configuration defines the various components of the project you want to manage:

{
  "components": [
    {
       "name": "someexamplecomponent",
       "repo": "my/localrepo",
       "tag": "latest",
       "command": ["/usr/bin/python", "/somedir/myapplication.py"],
       "ports": [
	         {"external": 8888, "container": 8888}
       ],
       "readyChecks": [
         { "kind": "http", "port": 8888 }
       ],
       "healthChecks": [
         { "kind": "http", "port": 8888, "path": "/some/path" }
       ],
       "volumesFrom": [
         "somedatacontainer"
       ],
       "bindings": [
         { "external": "/an/external/path", "volume": "/some/container/path"}
       ],
       "defineComponentLinks": [
         { "port": 8888, "name": "mycoolserver", "kind": "tcp" }
       ],
       "requireComponentLinks": [
         { "name": "anotherserver", "alias": "serveralias" }
       ],
       "environmentVariables": [
         { "name": "FOO", "value": "somevalue" }
       ]
    }
  ]
}

Field	Description	Default
name	The name of the component
repo	The docker image to use for the component
tag	The tag of the docker image to use	latest
user	The user under which to run the command in the container	(in image)
command	The command to run inside the container	(in image)
ports	Mappings of container ports to external ports
readyChecks	The various checks to run to ensure the container is ready (see below for list)
healthChecks	The various checks to run to ensure the container is healthy (see below for list)
terminationSignals	Signals which should be sent to a specific container when it should be shut down
terminationChecks	The various checks to run to ensure that the container is ready to be shut down	connections
volumesFrom	Container(s), by name, whose volume(s) should be mounted into the container
bindings	Mapping between external hosts paths and the corresponding container volumes
defineComponentLinks	Defines the component links exported by this component
requireComponentLinks	Defines the component links imported/required by this component
readyTimeout	Timeout in milliseconds that we will wait for a container to pass a ready check	10,000
environmentVariables	Environment variables to set when running the component's containers
privileged	Whether the container should run in privileged mode	False

Terminology

Project: Namespace that contains configuration for a set of components, as well as any metadata associated when those components are running. For example: 'frontend', 'backend', 'someproduct'.

Component: A named component that runs a specific docker image in a container. For example: 'elasticsearch', 'mongodb'.

Component Link: Similar to a Docker link: An exposed port by one component that is imported by one or more other components. Unlike a Docker link, a component link is managed by gantry and automatically updated via the proxy just link normal exposed ports. When a component link is required/imported by a container, the following environment variables are added into the containers for that component:

Environment Variable	Example Name	Example Value
{ALIAS}_CLINK	SERVERALIAS_CLINK	tcp://172.17.42.1:53852
{ALIAS}_CLINK_{PORT}_{KIND}	SERVERALIAS_CLINK_8888_TCP	tcp://172.17.42.1:53852
{ALIAS}_CLINK_{PORT}_{KIND}_PROTO	SERVERALIAS_CLINK_8888_TCP_PROTO	tcp
{ALIAS}_CLINK_{PORT}_{KIND}_ADDR	SERVERALIAS_CLINK_8888_TCP_ADDR	172.17.42.1
{ALIAS}_CLINK_{PORT}_{KIND}_PORT	SERVERALIAS_CLINK_8888_TCP_PORT	53852

Setting up a project

• Gantryd commands - distributed management
• Gantry commands - local management

Gantryd commands

Creating/updating the project's configuration

To setup a gantryd project, make sure that etcd is running, and gantry configuration is avaliable in some file.

Run the following to update the configuration for project myprojectname in gantryd:

sudo ./gantryd.py setconfig myprojectname myconfigfile

Response:

Configuration updated

Setup components by 'updating' them

To mark one or more components as ready for deployment, execute the following from a machine with the latest images:

sudo ./gantryd.py update myprojectname -c firstcomponent secondcomponent

Response:

Updating the image IDs on components
Component firstcomponent -> 4ae76210a4fe
Component secondcomponent -> 0cf0c034fc89

This sets the status of the components to 'ready' and associates them with the image IDs listed. Once run, any followup gantryd run commands on this machine (or any other machines in the etcd cluster) will update and start those components with those images.

Running components on machine(s)

Once components have been marked as ready, they can be run by executing gantryd run on one or more machines:

sudo ./gantryd.py run myprojectname -c firstcomponent secondcomponent

This command will start a daemon (and block), starting the components and monitoring them, until it is shutdown.

Updating a component across all listening machines

To tell components to update themselves in response to an image change, execute:

sudo ./gantryd.py update myprojectname -c firstcomponent secondcomponent

Response:

Updating the image IDs on components
Component firstcomponent -> 4ae76210a4fe
Component secondcomponent -> 0cf0c034fc89

The first machine running the gantryd daemon will start the update within 30 seconds.

Listing the status of all components

sudo ./gantryd.py list myprojectname

Response:

COMPONENT            STATUS               IMAGE ID
firstcomponent       ready                4ae76210a4fe
secondcomponent      stopped              0cf0c034fc89

Stopping a component on all machines

To tell components to stop themselves on all machines, execute:

sudo ./gantryd.py stop myprojectname -c firstcomponent secondcomponent

Response:

Marking components as stopped

All components specified will start the shutdown process within 30 seconds.

Killing a component on all machines

To order components to kill themselves immediately on all machines, execute:

sudo ./gantryd.py kill myprojectname -c firstcomponent secondcomponent

Response:

Marking components as killed

All components specified will be killed within 30 seconds.

Gantryd health checks

Gantryd supports a number of built-in checks for verifying that a container is properly started, running and healthy.

http Health Check

{ "kind": "http", "port": 8888, "path": "/somepath" }

Attempts to connect and download the HTTP page located at the given port and path. Fails if the HTTP response is not 2XX.

Note that "path" is optional.

tcp Health Check

{ "kind": "tcp", "port": 8888 }

Attempts to connect to the given port via TCP. Fails if the connection cannot be established.

###Gantry commands

gantry is the local version of gantry, intended for starting, stopping and updating of components on a single machine. Please note that you don't need etcd to be installed (or running) to use gantry.

Listing all containers running on a local machine for a component

sudo ./gantry.py myconfigfile list firstcomponent

Response:

CONTAINER ID         UPTIME               IMAGE ID             STATUS              
39d59e26ee64         Up 17 seconds        my/image:latest      running
18182e07ade1         Up 2 minutes         0cf0c034fc89         draining
87b14f60b220         Up 4 minutes         26c8cb358b9d         draining

Performing a local update of a component

Note: This will occur outside of the gantryd event loop, so this should only be used for single machine or canary images.

sudo ./gantry.py myconfigfile update firstcomponent

Response:

Starting container 39d59e26ee64
Waiting for health checks...
Running health check: http
Checking HTTP address: http://localhost:49320
Redirecting traffic to new container
Checking container statuses...
Updating proxy...
Starting monitoring...
Monitor check started

Note: If the -m flag is specified, then gantry will remain running and actively monitor the component's container, restarting it automatically if it becomes unhealthy.

Stopping all containers running on a local machine for a component

Note: This will drain containers in a safe way, so the process will block until all containers are free from incoming connections

sudo ./gantry.py myconfigfile stop firstcomponent

Response:

Draining all containers...
Checking container statuses...
Updating proxy...
Starting monitoring...
Monitor check started
Shutting down container: 39d59e26ee64
Proxy updated

Killing all containers running on a local machine for a component

sudo ./gantry.py myconfigfile kill firstcomponent

Response:

Draining all containers...
Killing container d05d73bc6c3
Checking container statuses...
Shutting down proxy...