The Celadon Cedar Stack

Last Updated: 13 March 2014

cedar stack

Table of Contents

Celadon Cedar is Heroku’s default runtime stack and is a flexible, polyglot environment with robust introspection and erosion-resistance capabilities. It embodies modern principles of building, deploying and managing web applications and is recommended for all apps.

Using Cedar

To create an app on the Cedar stack use the heroku create command from the Heroku command line:

$ heroku create
Creating quiet-sky-6888... done, stack is cedar |

Make sure you’re running version 2.1.0 or higher of the command-line tool which can be installed via the Heroku toolbelt.

$ heroku --version
$ heroku update
-----> Updating to latest client... done
$ heroku --version

Polyglot platform

Cedar is a polyglot platform with native support for many of today’s most popular and productive languages and frameworks including:

Get started with…
Ruby or Rails Node.js
Java, Spring or Play Python or Django
Clojure Scala

Polyglot support at the platform level lets development teams effectively utilize many languages across - and within - projects and ensures the right tool for the job. On Cedar, language choice and deployment infrastructure are orthogonal.

The foundation of Cedar’s unified multi-language support is the new process model which provides a consistent interface for running and managing apps.

Process model

Cedar introduces a new way to think about scaling your app: the process model. The process model is a generalized approach to managing processes across a distributed environment. It allows you to specify a custom list of process types in a Procfile and provides for very granular management of an application’s components.

web:     node web.js
worker:  node worker.js
reports: node report.js

The process model enables the thousands of unique dyno formations to be coordinated by the dyno manager while giving application developers the flexibility to use the frameworks and libraries of their choice.

Management granularity

The process model also allows applications with logical components to manage and scale at a very granular level. For instance, to dial-down HTTP processing while increasing background job concurrency, apply the heroku ps:scale command against your application’s unique process model.

$ heroku ps:scale web-1 worker+2 reports=1
Scaling web processes... done, now running 3
Scaling worker processes... done, now running 5
Scaling reports processes... done, now running 1

One-off dynos

Cedar’s flexibility is most evident with the heroku run command which lets you execute any command against your application. Many languages support a REPL which gives you a console with which to interact with your application. Use heroku run to establish an interactive session with a remote REPL for a Clojure app.

$ heroku run "lein repl"
Running lein repl attached to terminal... up, run.1
Clojure 1.3.0

One-off dynos, such as rake tasks for Ruby applications, can also be executed against their remote environment on Heroku.

$ heroku run rake db:migrate
Running `rake db:migrate` attached to terminal... up, ps.1
(in /app)
Migrating to CreateWidgets (20110204210157)
==  CreateWidgets: migrating ==================================================
-- create_table(:widgets)
   -> 0.0120s
==  CreateWidgets: migrated (0.0121s) =========================================


Deployment platforms can appear to be black-boxes in their management and automation of application runtimes. Heroku Cedar provides several tools to give application developers complete insight into their applications.

Dyno formation

The heroku ps command lists all dynos running for an application and clearly identifies the state of each individual dyno.

$ heroku ps
=== web: `bundle exec unicorn -p $PORT -c ./config/unicorn.rb`
web.1: up for 8h
web.2: up for 3m

=== worker: `bundle exec stalk worker.rb`
worker.1: up for 1m


Aggregated logs for all components in the application stack, including components managed by Heroku such as the HTTP router, are available in a single stream with heroku logs.

The -t flag keeps the log stream open so new entries are automatically displayed, much like the Unix tail -f command.

$ heroku logs -t
2012-03-16T14:02:57+00:00 heroku[router]: GET dyno=web.3  service=44ms status=200 bytes=32839
2012-03-16T14:02:57+00:00 app[worker.1]: [Worker(host:278fa1bc-d6aa-4409-bffd-0032dd0093b5 pid:1)] Article#reindex_without_delay completed after 0.1200
2012-03-16T14:02:57+00:00 app[worker.1]: [Worker(host:278fa1bc-d6aa-4409-bffd-0032dd0093b5 pid:1)] 1 job processed at 11.3892 j/s, 0 failed ...
2012-03-16T14:03:00+00:00 heroku[router]: GET dyno=web.1 service=2ms status=200 bytes=369
2012-03-16T14:03:05+00:00 app[web.3]: Started GET "/articles/git" for at 2012-03-16 14:03:05 +0000
2012-03-16T14:03:05+00:00 app[web.3]:   Processing by ArticlesController#show as HTML
2012-03-16T14:03:05+00:00 app[web.3]:   Parameters: {"id"=>"git"}
2012-03-16T14:03:05+00:00 app[web.3]: Read fragment views/ (3.6ms)

Additionally, several add-on providers provide retention, indexing and visualization capabilities of log data.

Here we see the router receiving a request and passing it to the web.3 dyno while the worker.1 dyno indexes an article for search. Router logs, database queries and application output is all coalesced into a singled event stream for full visibility into your application’s execution.

Component and dyno-level introspection is also available to quickly zero-in on problematic dynos and filter out irrelevant activity.

$ heroku logs --ps worker.1 -t
2012-03-16T14:16:58+00:00 app[worker.1]: [Worker(host:278fa1bc-d6aa-4409-bffd-0032dd0093b5 pid:1)] Article#reindex_without_delay completed after 0.0645
2012-03-16T14:16:58+00:00 app[worker.1]: [Worker(host:278fa1bc-d6aa-4409-bffd-0032dd0093b5 pid:1)] Article#record_view_without_delay completed after 0.0388
2012-03-16T14:16:58+00:00 app[worker.1]: [Worker(host:278fa1bc-d6aa-4409-bffd-0032dd0093b5 pid:1)] 10 jobs processed at 11.6378 j/s, 0 failed ...

Release management

All application deployments and configuration changes are captured and logged by Heroku and are made available with heroku releases.

$ heroku releases
Rel   Change                          By                    When
----  ----------------------          ----------            ----------
v52   Config add AWS_S3_KEY        5 minutes ago
v51   Deploy de63889           7 minutes ago
v50   Deploy 7c35f77           3 hours ago

Releases ensures that an application’s lifecycle is captured in an accountable and actionable format with the ability to undo errant modifications with heroku releases:rollback.

Advanced HTTP capabilities

On Cedar, an app named foo will have the default hostname of

The domain routes to a modern HTTP stack which offers a direct routing path to your web processes. This allows for advanced HTTP uses such as chunked responses, long polling, and using an async webserver to handle multiple responses from a single web process.

Cedar does not include a reverse proxy cache such as Varnish, preferring to empower developers to choose the CDN solution that best serves their needs.

Migrating to Cedar

Migrating from Bamboo to Cedar allows an application to take advantage of a much more flexible and powerful stack. Because the significant architectural differences, migrating to Cedar is a largely manual process.

Instructions for migrating to Cedar can be found here.