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Capitan

GoDoc

Capitan is a tool for managing multiple Docker containers based largely on crowdr

Capitan is only a wrapper around the docker cli tool, no api usage whatsoever (well... an inspect command here and there). This means it will basically work with all versions of docker.

$ capitan up

Run arguments changed, doing blue-green redeploy: capitan_redis_green_1
Running capitan_redis_blue_1
cd939956f332391489d0383610d9da2c420595d495934c3221376dbf68854316
Removing old container capitan_redis_green_1...
Already running capitan_mongo_blue_1
Already running capitan_nats_blue_1
Already running capitan_app_blue_1

Features

  • Provides commands which operate on collection of containers.
  • Uses predefined description of containers from readable configuration file.
  • Can use any docker run option that is provided by your docker version.
  • The order of starting containers is defined in configuration file.
  • The order of stopping containers is the reverse of the order of starting.
  • Easy to install, compiled static go binaries available for linux, and mac. It doesn't require any execution environment or other libraries.
  • Allows the use of bash as hooks for many capitan commands.
  • Blue/Green deployment - option to only remove original container when starting new version of same container if it starts and passes hook commands.

Installation

Head over to the releases page to download a pre-build binary or deb file.

Or using go:

go get github.com/byrnedo/capitan

Commands

Invasive commands

up

Create then run or update containers Recreates if:

  1. If newer image is found it will remove the old container and run a new one No longer does this as capitan can't know which node to check images for when talking to a swarm.
  2. Container config has changed

Starts stopped containers

capitan up
# Optionally can attach to output using `--attach|-a` flag.
capitan up -a

create

Create but don't run containers

capitan create

start

Start stopped containers

capitan start
# Optionally can attach to output using `--attach|-a` flag.
capitan start -a

scale

Start or stop instances of a container until required amount are running

# run 5 instances of mysql
capitan scale mysql 5

NOTE: for containers started via this command to be accepted by further commands, the config output must be altered to state the required instances

restart

Restart containers

capitan restart
# Further arguments passed through to docker, example `capitan start -t 5`
capitan restart -t 10
stop

Stop running containers

capitan stop
# Further arguments passed through to docker, example `capitan stop -t 5`
capitan stop -t 10
kill

Kill running containers using SIGKILL or a specified signal

capitan kill
# Further arguments passed through to docker, example `capitan kill --signal KILL`
capitan kill --signal KILL
rm

Remove stopped containers

capitan rm
# Further arguments passed through to docker, example `capitan rm -f`
capitan rm -fv

Non invasive commands

ps

Show container status

- Further arguments passed through to docker, example `capitan ps -a`
ip

Show container ip addresses

logs

Follow container logs

pull

Pull images for all containers

build

Build any containers with 'build' flag set (WIP)

Configuration

Global options

 --cmd, -c "./capitan.cfg.sh"	Command used to obtain config
 --debug, -d				    Print extra log messages
 --dry-run, --dry			    Preview outcome, no changes will be made
 --filter, -f 		            Filter to run action on a specific container only
 --help, -h				        Show help
 --version, -v			        Print the version

Config file/output

Service config is read from stdout of the command defined with --cmd .

capitan by default runs the command ./capitan.cfg.sh in the current directory to get the config. This can be customized with --cmd|-c flag.

capitan --cmd ./someotherexecutable <some action>

You could use any command which generates a valid config. It doesn't have to be a bash script like in the example or default.

Filtering

A single service type can specified for an action by using the --filter|-f flag. So if your conf looked like this:

...
fooapp hostname blah
...

You could filter any command to run on just that service type by doing:

capitan --filter fooapp <some action>

Global options

global project

The project name, defaults to current working directory

global project_sep

String to use to create container name from project and name specified in config

global blue_green [true/false]

String to deploy using blue/green handover. Defaults to false. This can be turned on/off per container with

CONTAINER_NAME blue-green [true/false]

global hook [hook name] [hook command]

Allows for a custom shell command to be evaluated once at the following points:

  • Before/After up (before.up, after.up)
    • This occurs during the up command
  • Before/After Start (before.start, after.start)
    • This will occur in the start command
  • Before/After Stop (before.stop, after.stop)
    • This will occur in the stop command
  • Before/After Kill (before.kill, after.kill)
    • This will occur in the kill command
  • Before/After Rm (before.rm, after.rm)
    • This will occur in the rm command

Container Options

The output format must be:

CONTAINER_NAME COMMAND [ARGS...]

All commands are passed through to docker cli as --COMMAND EXCEPT the following:

build

This allows a path to be given for a dockerfile. Note, it will attempt to build every time. Use build-args and pass --no-cache to force a full clean build each time.

build-args

Any further arguments that need to be passed when building.

hook [hook name] [hook command]

Allows for a custom shell command to be evaluated at the following points for each container

  • Before/After Run (before.run, after.run)
    • This occurs during the up command
  • Before/After Start (before.start, after.start)
    • This will occur in the up, start and restart command
  • Before/After Stop (before.stop, after.stop)
    • This will occur in the stop command only
  • Before/After Kill (before.kill, after.kill)
    • This will occur in the kill command only
  • Before/After Rm (before.rm, after.rm)
    • This will occur in the up and rm command

NOTE hooks do not conform exactly to each command. Example: an up command may rm and then run a container OR just start a stopped container.

scale

Number of instances of the container to run. Default is 1.

NOTE: this is untested with links ( I don't use links )

link

An attempt to resolve a link to the first instance of a container is made. Otherwise the unresolved name is used.

WARNING: When scaling, if the link resolves to a container defined in capitan's config, it will always resolve to the first instance. For example: app link mycontainer:some-alias will always resolve to <project>_mycontainer_1

rm

By default capitan runs all commands with -d. This flag makes capitan run the command with -rm instead.

WARNING: This feature is experimental and may result in unexpected failures. A more predictable way is to leverage docker wait along with a dynamic label. For example:

mycontainer label $(date +%s)
mycontainer hook after.run docker wait \$CAPITAN_CONTAINER_NAME

volumes-from

An attempt to resolve a volume-from arg to the first instance of a container is made. Otherwise the unresolved name is used.

WARNING: When scaling, if the container name resolves to a container defined in capitan's config, it will always resolve to the first instance. For example: app volumes-from mycontainer will always resolve to <project>_mycontainer_1

Environment Variables

The following environment variables are available when creating the containers and when running container hooks

# container name
CAPITAN_CONTAINER_NAME
# container type 
CAPITAN_CONTAINER_SERVICE_TYPE
# instance of this type,eg if you have scale = 5 then each container will have their own instance number from 1 -> 5
CAPITAN_CONTAINER_INSTANCE_NUMBER
# the project name
CAPITAN_PROJECT_NAME

The following environment variables are available to all hook scripts

CAPITAN_PROJECT_NAME
CAPITAN_HOOK_NAME

For example, following capitan.cfg.sh

#!/bin/bash

cat <<EOF
global project test

mysql name mymysql
mysql label containerName=\$CAPITAN_CONTAINER_NAME
mysql label containerServiceName=\$CAPITAN_CONTAINER_SERVICE_NAME
mysql label containerInstanceNumber=\$CAPITAN_CONTAINER_INSTANCE_NUMBER
mysql label projectName=\$CAPITAN_PROJECT_NAME
mysql hook after.run echo "hook: \$CAPITAN_HOOK_NAME: ran \$CAPITAN_CONTAINER_NAME in project \$CAPITAN_PROJECT_NAME"
EOF

Would result in the following run command:

docker run -d --name test_mysql_1 
    --label containerName=test_mysql_1 
    --label containerServiceName=mysql
    --label containerInstanceNumber=1
    --label projectName=test

And the following hook ouput

Running test_mysql_1
34e7fffb937c3154c2a963ee605c7958404aa5d80519db4ef3d2a80a06974021
hook: after.run: ran test_mysql_1 in project test

Note that the $ must be escaped if using HEREDOC or double quotes in bash.

Example Config

Check out dev-stack for an example. Clone it and just run capitan --dry up.

Or check out the ./example dir.

Also, here's something to whet your appetite:

#!/bin/bash
PREFIX=dev

cat <<EOF
#
# General redis container
#
redis image redis:latest
redis hostname ${PREFIX}_redis
redis publish 6379
redis hook after.run echo "look everyone, I ran \$CAPITAN_CONTAINER_NAME" && sleep 3
redis hook after.start sleep 3

#
# General mongodb container
#
mongo image mongo:latest
mongo command mongod --smallfiles
mongo hostname ${PREFIX}_mongo
mongo publish 27017

#
# My app
#
app build ./
app publish 80
app link redis
app link mongo:mongodb
EOF

Roadmap

  1. Tests
  2. More efficient up logic
  3. Helpful aliases in shell env.
  4. More flexible build command

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Capitan is a tool for managing multiple Docker containers

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