A talk I gave at North West Ruby User's Group (http://nwrug.org/) August 20th 2009

1. Capistrano at your command
Tips and tricks, from wimp to winner
Lee Hambley - August 20th 2009
1

2. What’s on the menu?
✤ Capistrano’s Structure
✤ Net::SSH
✤ The Scope of Execution
✤ Task chaining; your own multi-stage
✤ Streams
✤ Prompts
2

3. Simply put, Capistrano is a tool for automating
tasks on one or more remote servers. It executes
commands in parallel on all targeted machines,
and provides a mechanism for rolling back
Capistrano changes across multiple machines. It is ideal for
anyone doing any kind of system administration,
either professionally or incidentally.
What’s in the Box?
Net::SSH Net::SFTP Net::SCP
Net::SSH::Gateway
$ gem dependency capistrano
Gem capistrano-2.5.8
Capistrano’s Structure net-ssh (>= 2.0.10, runtime)
net-sftp (>= 2.0.0, runtime)
net-scp (>= 1.0.0, runtime)
net-ssh-gateway (>= 1.0.0, runtime)
3

4. Simply put, Capistrano is a tool for automating
tasks on one or more remote servers. It executes
commands in parallel on all targeted machines,
and provides a mechanism for rolling back
Capistrano changes across multiple machines. It is ideal for
anyone doing any kind of system administration,
either professionally or incidentally.
What’s in the Box?
✤ Consistent support for different source
control software.
Net::SSH Net::SFTP Net::SCP
Net::SSH::Gateway
$ gem dependency capistrano
Gem capistrano-2.5.8
Capistrano’s Structure net-ssh (>= 2.0.10, runtime)
net-sftp (>= 2.0.0, runtime)
net-scp (>= 1.0.0, runtime)
net-ssh-gateway (>= 1.0.0, runtime)
3

5. Simply put, Capistrano is a tool for automating
tasks on one or more remote servers. It executes
commands in parallel on all targeted machines,
and provides a mechanism for rolling back
Capistrano changes across multiple machines. It is ideal for
anyone doing any kind of system administration,
either professionally or incidentally.
What’s in the Box?
✤ Consistent support for different source
control software.
Net::SSH Net::SFTP Net::SCP ✤ Rake-esque task definitions, including
before/after callbacks for method
chaining.
Net::SSH::Gateway
$ gem dependency capistrano
Gem capistrano-2.5.8
Capistrano’s Structure net-ssh (>= 2.0.10, runtime)
net-sftp (>= 2.0.0, runtime)
net-scp (>= 1.0.0, runtime)
net-ssh-gateway (>= 1.0.0, runtime)
3

6. Simply put, Capistrano is a tool for automating
tasks on one or more remote servers. It executes
commands in parallel on all targeted machines,
and provides a mechanism for rolling back
Capistrano changes across multiple machines. It is ideal for
anyone doing any kind of system administration,
either professionally or incidentally.
What’s in the Box?
✤ Consistent support for different source
control software.
Net::SSH Net::SFTP Net::SCP ✤ Rake-esque task definitions, including
before/after callbacks for method
chaining.
Net::SSH::Gateway
✤ Ability to detect and rollback broken jobs
using transactions
$ gem dependency capistrano
Gem capistrano-2.5.8
Capistrano’s Structure net-ssh (>= 2.0.10, runtime)
net-sftp (>= 2.0.0, runtime)
net-scp (>= 1.0.0, runtime)
net-ssh-gateway (>= 1.0.0, runtime)
3

7. Simply put, Capistrano is a tool for automating
tasks on one or more remote servers. It executes
commands in parallel on all targeted machines,
and provides a mechanism for rolling back
Capistrano changes across multiple machines. It is ideal for
anyone doing any kind of system administration,
either professionally or incidentally.
What’s in the Box?
✤ Consistent support for different source
control software.
Net::SSH Net::SFTP Net::SCP ✤ Rake-esque task definitions, including
before/after callbacks for method
chaining.
Net::SSH::Gateway
✤ Ability to detect and rollback broken jobs
using transactions
✤ Roles, :app, :web, :db & :define-your-own
$ gem dependency capistrano
Gem capistrano-2.5.8
Capistrano’s Structure net-ssh (>= 2.0.10, runtime)
net-sftp (>= 2.0.0, runtime)
net-scp (>= 1.0.0, runtime)
net-ssh-gateway (>= 1.0.0, runtime)
3

8. Net::SSH
✤ Magical pure-Ruby
implementation of the SSH
protocol.
✤ Honours your ~/ssh/config
settings.
✤ Supports (creating and using)
Tunnels, Gateways, Agent
Forwarding and more...
✤ Super clean syntax...

9. Net::SSH
✤ Magical pure-Ruby
implementation of the SSH
protocol.
✤ Honours your ~/ssh/config
settings.
✤ Supports (creating and using)
Tunnels, Gateways, Agent
Forwarding and more...
✤ Super clean syntax...

10. Net::SSH
✤ Magical pure-Ruby
implementation of the SSH
protocol.
✤ Honours your ~/ssh/config
settings.
✤ Supports (creating and using)
Tunnels, Gateways, Agent
Forwarding and more...
✤ Super clean syntax...

11. The Scope of Execution
✤ What runs where?
✤ What permissions will I need?
✤ Obscure errors about permissions?
✤ .. lots of different things happening

12. The Scope of Execution
$ → cap deploy
Calling another Capistrano task.
* executing `deploy'
* executing `deploy:update' Transactions, you can define what to do for
your own transactions if a task within it fails.
** transaction: start
{
* executing `deploy:update_code' A shell command run on your workstation.
executing locally: "git ls-remote git@github.com:leehambley/
capistrano-website.git HEAD"
A shell command run remotely.
* executing "git clone -q git@github.com:leehambley/capistrano-
website.git /u/apps/capistrano-website/releases/20090820114515 && ...... "
{
* executing `deploy:finalize_update' A shell command run remotely, connecting
to your repository server. †
* executing "chmod -R g+w /u/apps/capistrano-website/releases/
20090820114515"
{
* executing `deploy:symlink'
* executing "rm -f /u/apps/capistrano-website/current && ln -s /u/apps/
capistrano-website/releases/20090820114515 /u/apps/capistrano-website/
current"
** transaction: commit † Requires passwordless access to your repository
server from your servers; this can be either keys (GitHub
deploy keys feature) or SSH agent forwarding to provide
your own key by proxy

13. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features

14. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features
➊ ➋
$ cap check-ruby-version deploy

15. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features -----------------
➊ ➋
$ cap check-ruby-version deploy

16. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features -----------------
➊ ➋
$ cap check-ruby-version deploy
capture
Executes a command on a single host and returns
("captures") the output as a string.
stream
Very similar to run, but optimised for displaying
live streams of text (like tailed log files) from
multiple hosts.
run
Execute commands on one or more servers

17. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features -----------------
➊ ➋
$ cap check-ruby-version deploy
➊ ➋ ➌
$ cap staging check-ruby-version deploy
capture
Executes a command on a single host and returns
("captures") the output as a string.
stream
Very similar to run, but optimised for displaying
live streams of text (like tailed log files) from
multiple hosts.
run
Execute commands on one or more servers

18. Task Chaining
➊ ➋ ➌
$ rake db:migrate spec features -----------------
➊ ➋
$ cap check-ruby-version deploy
➊ ➋ ➌
$ cap staging check-ruby-version deploy
capture
Executes a command on a single host and returns
("captures") the output as a string.
stream
Very similar to run, but optimised for displaying
live streams of text (like tailed log files) from
multiple hosts.
run
Execute commands on one or more servers

19. Streams?
In Unix and Unix-like operating systems, as well as certain
programming language interfaces, the standard streams are
pre-connected input and output channels between a
computer program and its environment (typically a text
terminal) when it begins execution. The three I/O
connections are called standard input, standard output and
standard error.

20. Streams?
In Unix and Unix-like operating systems, as well as certain
programming language interfaces, the standard streams are
pre-connected input and output channels between a
computer program and its environment (typically a text
terminal) when it begins execution. The three I/O
connections are called standard input, standard output and
standard error.

21. Streams?
In Unix and Unix-like operating systems, as well as certain
programming language interfaces, the standard streams are
pre-connected input and output channels between a
computer program and its environment (typically a text
terminal) when it begins execution. The three I/O
connections are called standard input, standard output and
standard error.

22. Prompts
Implementation

23. Prompts
Implementation

24. Prompts
Implementation

25. Resources
✤ Capistrano Wiki: - http://www.capify.org/
✤ Bash Hackers Wiki: - http://bash-hackers.org/wiki/
✤ Questions: - lee.hambley@gmail.com
✤ Support: - irc://freenode.org/capistrano
✤ Mailing List: - http://groups.google.com/group/capistrano
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26. Questions?