Dokku adheres to the philosophy that application resources should be handled as separate components from the actual application. This creates a flexible relationship where resources or main application code can be swapped out easily without much additional configuration. Dokku handles outside resources through a plugin system.
In this guide, we will discuss how to utilize Dokku's plugin system to extend the functionality of the project and link your application with the backends that it needs. We will also look into some other plugins that can help you monitor and manage your applications.
The main thing most people will want out of the plugin system is
database access. Through community plugins, Dokku provides access to
many popular database systems including MariaDB, PostgreSQL, MongoDB, and Redis. You can find a full list of database
Beyond database access, there are plugins for multiple process managers. Dokku runs processes through a "Procfile", which lists the process types that must be run and the commands that are needed to execute them. By default, Dokku only runs "web" processes.
To run other types of processes (like workers), you can use a process manager, which runs the Procfile to execute other process types. There are multiple ones to choose from, but they all basically do the same thing. The current selection includes circus, shoreman, and supervisord. On top starting additional process types, some of these also have the ability to restart crashed applications.
Additionally, there are some other interesting plugins that may help your application run smoother. For instance, there is a plugin called user-env-compile which will provide your build environment with environmental variables that are usually not set until the deploy stage.
After that, you download the plugin code with a simple git clone:
git clone git_repository optional_alternative_plugin_name
After that, you can install the plugins and configure them to your environment with the following command:
This will grab all of the necessary dependencies using
apt-get and configure your environment. It will then install any plugins that have not been installed.
You can access Dokku's help system by typing:
Dokku's help system is dynamically generated to include the help files packaged with plugins. As a result, if you install the PostgreSQL plugin for instance, you will get new entries describing its usage:
. . . postgresql:create <app> Create a PostgreSQL container postgresql:delete <app> Delete specified PostgreSQL container postgresql:info <app> Display database informations postgresql:link <app> <db> Link an app to a PostgreSQL database postgresql:logs <app> Display last logs from PostgreSQL container . . .
This means that no matter how many plugins you install, your
documentation will still all be in one place. It is always a good idea
dokku help after installing a new plugin.
Next, go to the project's page to see how they recommend installing it. Some plugins clone their files into a directory with a different name than the GitHub name. The PostgreSQL plugin's page uses the name "postgresql" after the clone command:
git clone https://github.com/Kloadut/dokku-pg-plugin postgresql
Install the plugin components and their dependencies:
For instance, the PostgreSQL plugin allows you to create the database instance prior to deployment. However the MongoDB plugin requires you to deploy your application, create the database, and then repush the application.
The PostgreSQL plugin is pretty flexible. It can handle either situation, but it's one less step if you create the database first.
Creating the Database First
If you are creating the database first and want it to be automatically linked to your application on deployment, you need to select the same name for your database that you plan on using for your application. The general syntax for PostgreSQL is:
dokku postgresql:create app_name
Dokku will then link any application pushed with the name
app_name to the database instance.
When you create the database, you will usually receive some information about the connection parameters. In our example, the connection parameters would look something like:
-----> PostgreSQL container created: postgresql/app_name Host: 111.222.333.444 User: 'root' Password: 'ClUzB4nRhEWgjiVt' Database: 'db' Public port: 49187
If you need to hard code the connection parameters in your app (rarely recommended), you can use this information. You could also use this information to connect to the database on the local machine through the usual database interfaces (psql in this case), and pre-populate data.
In most cases, you will never need to use this information, because
upon deployment, Dokku sets an environmental variable called
which contains a connection string with the appropriate parameters.
You can access this variable and use it in your program to maintain
If you do need to access this information, you can always recall it by typing:
dokku postgresql:info app_name
Now that we have a database created for our application, we would push our application to Dokku as normal using git. In the output that follows, towards the end, you should be able to see that your application is linked with your database correctly:
remote: -----> App app_name linked to postgresql/app_name database remote: DATABASE_URL=postgres://root:ClUzB4nRhEWgjiVt@111.222.333.444/db
As you can see, the
DATABASE_URL variable has been set using the database information we discussed earlier.
If you are experiencing database issues, most plugins maintain their own logs:
dokku postgresql:logs app_name
Deploying the App First
If you wish to deploy an application with a database with a different name than your application, or if you forgot to deploy the database before deploying the application, you can always link the database afterward.
In this case, you can do one of two things. If you simply forgot to create the database, you can simply issue the normal create database command with a matching name:
dokku postgresql:create app_name
Afterwards, you can re-push your application because the
DATABASE_URL variable is created during application deployment.
However, you can also just link it. This is also necessary if you would like to use a different name for you database, you can create it and then link it:
dokku postgresql:create database_name (By this point, your application must be deployed) dokku postgresql:link app_name database_name
This will link the database to the application so that your program will function correctly.
If you find that Dokku is missing some functionality that you need, consider making a plugin yourself. If you create a plugin for Dokku, you can edit the Dokku plugins page to feature your plugin.
Article ID: 219
Created On: Sun, Dec 29, 2013 at 8:40 PM
Last Updated On: Sun, Dec 29, 2013 at 8:40 PM
Authored by: ASPHostServer Administrator [firstname.lastname@example.org]
Online URL: http://faq.asphosthelpdesk.com/article.php?id=219