Beer Garden Documentation

The goal of this section is to help you write a remote plugin from scratch. In order to write remote plugins there are a few things that you need.

Prerequisites

In order to build a plugin you’ll need a functioning Python environment. Setting that up is outside the scope of this tutorial; we recommend pyenv. You’ll also need access to a functioning Beer Garden. Check out the installation instructions for ways to stand up your own Beer Garden.

The simplest way to get started is to use the utility package we’ve created to make plugin building as easy as possible. The package is called brewtils and lives on PyPI. You can find Brewtils API Documentation here. Add it to your environment like this:

pip install brewtils

Don’t forget, if you’re writing a remote plugin, you’ll need to be able to access the Beer Garden REST Service

Now you’re ready to start writing your plugin.

Hello World!

This section will take you through setting up a simple Hello, World example.

Write the code

Plugins are basically just classes that you would like to expose over the network. So let’s create a simple, and classic "Hello, World!" example. Use your favorite text editor and open up a file called plugin.py and add the following:

plugin.py

from brewtils import Plugin, command


class HelloWorldClient(object):

    @command (1)
    def say_hello(self):
        greeting = "Hello, World!"

        print(greeting)

        return greeting


def main():
    client = HelloWorldClient()

    plugin = Plugin(
        client=client,
        name="hello-world", (2)
        version="1.0.0",
        description="My First Plugin",
        bg_host="<HOST>", (3)
        bg_port="<PORT>",
        ssl_enabled=<SSL_ENABLED>,
    )
    plugin.run()


if __name__ == "__main__":
    main()

1	The `@command` decorator marks this method as a Command that’s part of the enclosing Client.
2	The values defined here determine how the plugin is listed in the UI.
3	Be sure to replace `<HOST>`, `<PORT>`, and `<SSL_ENABLED>` with appropriate values for your garden.

To review what’s happening here: we added an import Plugin at the top of our file and created a standard main method. In that method we created a HelloWorldClient object and a Plugin object. Notice that when we create the Plugin we pass it the client and some additional parameters. Don’t worry too much about the additional paramters - we’ll cover them later.

That’s all the code you need!

Run the code

Run the plugin like this:

python plugin.py

It will start up and print some logging showing the plugin registering with Beer Garden. Congratulations! You’ve just deployed your first plugin!

Use the code

At this point you should see your plugin on the Systems page in Beer Garden. Click the big blue Explore button next to hello-world to see a list of all commands available for the Plugin you made.

Since we only defined one command as part of this tutorial the only command listed should be the say_hello command. Click the Make it Happen! button to go to the page for that command.

The command page is where you can specify options and customization for individual executions of that command. Since we didn’t define any options (this command always prints 'Hello World!') the only customization available is the comment field. You can add free-form text here and it will be included as part of the request you’re about to generate.

Are you ready? Click the Make Request button once you’re ready.

Making a request takes you to the Request page for the request you just generated. You can see the unique ID as part of the page title. You should see the status start as IN PROGRESS and then change to SUCCESS once the request completes. Also notice that the output changes when the request is finished.

If you didn’t catch those changes on the first try, don’t worry. Use the Pour it Again button in the top-right corner to go back to the command screen you just left. From here you can use the Make Request button to make another request.

This command doesn’t have any parameters, but for commands that do the Pour it Again button will default them to exactly how they were for the original request.

Stop the code

The best way to stop a plugin is to use the Systems Management page to send a stop message. In Beer Garden find the Systems option under the Admin menu. Then click the stop icon next to the hello-world listing.

You should see your plugin log that it has terminated and stop executing, and if you go to the Admin → Systems page in Beer Garden you should see the hello-world plugin is 'STOPPED'.

You can also use Ctrl-c to stop the plugin from the terminal. This works, but it doesn’t tell Beer Garden that the plugin is stopping. You’ll still see the plugin terminate and stop executing, but the status in Beer Garden will still be 'RUNNING'. After a short period the status will change to 'UNRESPONSIVE'.

Exception Handling

It is important to be able to tell Beer Garden when something on your system goes wrong. brewtils takes advantage of Python’s exceptions in order to handle command malfunctions. So if you have a function:

def my_error(self):
    raise ValueError("Something went wrong!")

This will result in the request status turning to "ERROR" and its output will be Something went wrong!. It is expected that plugins will throw errors as a way to notify Beer Garden that something has gone wrong.

If you choose to handle errors and not throw, you will notice something that may be quite confusing to your plugins users. Let’s have an example:

def my_error(self, x):
  if x is None:
    # This is actually an error, but we will short-circuit
    return "An error occurred."
  return x

If x being None is an error, then you should throw an error. Otherwise, the request will be marked as SUCCESS while the output will say An error occurred

If your command has a JSON output type, then Beer Garden will attempt to format your exception as a JSON error message. Here’s an example:

@command(command_type="JSON")
def my_error(self):
  raise ValueError("Error Message")

If you call this method, you’ll still notice a status of ERROR but the output will be something like:

{
  "message": "Error Message",
  "attributes": {}
}

If you’re asking what the attributes entry is supposed to represent, it will take the dict of the exception and attempt to jsonify it. Let’s say you have a custom exception class like the following:

class MyError(Exception):
  def __init__(self, *args, **kwargs):
    self.foo = kwargs.pop("foo")
    self.bar = kwargs.pop("bar")

Then you throw that error during a command, Beer Garden will modify the output as per the following:

{
  "message": "Error Message"
  "attributes": {"foo": "foo_value", "bar": "bar_value"}
}

If your attributes are not JSON serializable, then a string representation of the dictionary will be provided to the attributes.

Making your plugin more descriptive

In order to help users of Beer Garden understand how to utilize your plugin, you’ll need to provide some basic information about your plugins. There are lots of ways to specify lots of different information that your plugin can do. So we’ll take it one at a time.

Adding a command description

There are two ways you can add a description to your command. One way is by using pydoc comments

Pydoc example

class HelloWorldClient(object):

  @command
  def hello_world(self):
    """Prints Hello, World!"""
    print("Hello, World!")

The description will only take the first line of your comment

Or you can specify a description via the @command decorator

class HelloWorldClient(object):

  @command(description="Prints Hello, World!")
  def hello_world(self):
    print("Hello, World!")

Describing a parameter

Obviously, most methods will have required arguments. You can utilize the @parameter decorator to describe the argument as in the following:

class HelloWorldClient(object):

  @command(description="Echos the message you pass to it")
  @parameter(key="message",
                description="Message to print and return")
  def echo(self, message):
    print(message)
    return message

@parameter only requires the key option be passed to it. The key must match the parameter’s name in the method. There are lots of different options when considering the @parameter. Check out the following table for a high- level summary:

Table 1. Plugin Param Arguments
Argument	Required?	Options	Default	Description
key	Y	N/A	N/A	Specifies the Argument Name
type	N	[String, Integer, Float, Boolean, Any, Dictionary, Base64]	Any	Specifies the type of Parameter
multi	N	[True, False]	False	Specifies if the parameter is a list
display_name	N	N/A	key	Specifies a Pretty way to refer to the key
optional	N	[True, False]	False	Specifies if the parameter is required
default	N	N/A	N/A	The Default value of the Parameter
description	N	N/A	N/A	A short Description of the Parameter
choices	N	N/A	N/A	A list of possible values
is_kwarg	N	N/A	N/A	If parameter comes in as a kwarg
model	N	N/A	N/A	A python Object that has a parameters list
nullable	N	[True, False]	False	Specifies if this parameter can be null
maximum	N	Integer	N/A	Specifies maximum (See detailed for more info)
minimum	N	Integer	N/A	Specifies minimum (See detailed for more info)
regex	N	N/A	N/A	Specifies regex to validate against this value
form_input_type	N	[textarea]	N/A	Specifies the form type to render for this plugin

Key argument

The key argument to @parameter is the only required parameter. It must match the name of an argument in whatever method it is decorating. This is how users of your plugin will identify the parameter they would like to set.

Key argument example

@parameter(key="message")
def do_something(self, message):
    print(message)
    return message

Type argument

Setting the type field for a Parameter will let Beer Garden do a couple of things.

First, it lets Beer Garden perform type validation on that parameter. If the value does not match the type (and can’t be converted sensibly) then the Request will be rejected.

Second, it allows the UI to use the best form element for that type of data. For example, you could use a string to represent a date, but setting type to 'date' means the UI will use a nice datepicker form element.

Finally, several validation constraints can only be applied to specific types. The minimum and maximum constraints are good examples of this - they don’t make sense for booleans, but they definitely do for integers!

Type argument example

@parameter(key="number", type="Integer")
def multiply_by_zero(self, number):
    return number * 0

This table outlines the valid type options.

Type Valid Constraints Notes

Type	Valid Constraints	Notes
String	minimum, maximum, regex	Minimum and Maximum refer to length
Integer	minimum, maximum
Float	minimum, maximum
Boolean
Date		Form control will not have 'time' option
DateTime
Dictionary		JSON Object
Base64		Allows the user to upload a file as a parameter. This is provided as a file-like object to the plugin.
Any		Valid JSON (Object, Array, String), number, literal `null`, `true`, `false`

String

minimum, maximum, regex

Minimum and Maximum refer to length

Integer

minimum, maximum

Float

minimum, maximum

Boolean

Date

Form control will not have 'time' option

DateTime

Dictionary

JSON Object

Base64

Allows the user to upload a file as a parameter. This is provided as a file-like object to the plugin.

Any

Valid JSON (Object, Array, String), number, literal null, true, false

The default type is Any. This gives the most flexibility, but it’s a good idea to always specify a type to take advantage of the benefits described above.

Multi argument

The multi field let’s Beer Garden know that the parameter should be a list. Most of the other fields stay the same and continue to describe the individual items in the list.

Multi argument example

@parameter(key="list_of_strings", multi=True, type="String")
def do_something(self, list_of_strings):
    for s in list_of_strings:
        print(s)

Some of the fields do change meaning when you’ve specified that multi is true. See the below table for a more detailed description.

Table 2. Multi Changes These Arguments
Argument	How is it changed?
choices	Choices specify the only valid values, no value can be repeated.
maximum	Specifies Maximum length of the list
minimum	Specifies Minimum length of the list

Display name argument

The display_name field allows you control over how Beer Garden renders the name of the field. This is useful if your argument has a less-than-useful name from the end-users perspective.

Display name argument example

@parameter(key="foo", display_name="Name")
def do_something(self, foo):
    print("Hi!, my name is: %s" % foo)

Optional argument

The optional field allows you to specify whether or not the parameter is optional or required. The default depends on if there is a default value in the method definition.

Optional argument example

@parameter(key="foo", optional=True, nullable=True))
def do_something(self, foo):
    # By default, foo would not be optional but
    # it is specified in the param so it's assumed
    # the developer will handle the None case.
    if foo is None:
        print("foo is empty!")
    else:
        print(foo)

If a default is passed in, then optional will be set to True by default.

If you specify that something is optional, then it must also be nullable if no default is specified.

Default argument

The default field allows you to specify the default value for a parameter if it is not given by a user. If there is a default value in the method definition then it will use that.

Default argument example

@parameter(key="foo")
def do_something(self, foo="bar"):
  print(foo)

In the above case, if someone utilizes this command but does not pass Beer Garden the foo parameter, then Beer Garden will default it to bar. Below is another example of how to use the default argument.

Default argument example

@parameter(key="foo", default="bar"))
def do_something(self, foo):
    print(foo)

These are functionally equivalent for Beer Garden.

Description argument

The description field adds a description to the plugin parameter you are defining.

Description argument example

@parameter(key="foo", description="Your first name")
def do_something(self, foo):
    pass

Choices argument

The choices field allows you to specify possible values for a parameter.

Basic Usage

The easiest way to use choices is to pass a list of values:

Choices list example

@parameter(key="output_type", choices=["json", "xml"])
def format(self, obj, output_type):
    if output_type == "json":
        return jsonify(obj)
    elif output_type == "xml":
        return xmlify(obj)

Sometimes it’s useful to have the display text (what shows up in the UI) be different from the 'real' value (what gets sent to the plugin). To do this, instead of a list of literal values just pass a list of objects with text and value keys:

Choices rename example

@parameter(key="output_type", choices=[
    {"text": "The best", "value": "json"},
    {"text": "The worst", "value": "xml"}])
def format(self, output_type):
    pass

Additional Configuration

There are some configuration options that control how choices works. Beer Garden will pick sensible defaults, but to tweak them pass a dictionary to choices:

Choices Dictionary example

@parameter(key="output_type",
           choices={'type': 'static', 'value': ['json','xml']})
def format(self, output_type):
    ...

That way you can add additional key/value pairs to the choices dictionary.

Choices Type

You probably noticed the 'type': 'static' entry above. Beer Garden is able to figure out exactly what to do when you pass a list of values to choices, but it needs a hint when you use the dictionary configuration. There are a couple of other ways to populate the choices list (more on those in a bit) so you need to be explicit.

The example above is using the static type, which tells Beer Garden to expect a list of values in the value attribute. This is functionally identical to passing a list of values to choices directly.

The other choice types will be explained in detail in the Choice Sources section.

Display

When you use choices the UI form control can be a typeahead or a select. To specify which to use just set the display key:

Choices Typeahead example

@parameter(key="output_type",
           choices={'type': 'static', 'value': ['json','xml'],
                    'display': 'typeahead'})
def format(self, output_type):
    ...

Strictness

The strict configuration controls whether values that aren’t explicitly listed are allowed. Setting strict to False will result in a typeahead control that will use the choices values but still allow any text to be submitted.

Choices Non-strict example

@parameter(key="output_type",
           choices={'type': 'static', 'value': ['json','xml'],
                    'strict': False})
def format(self, output_type):
    ...

Setting strict to False for a select won’t affect the display, but the strict value also controls validation on the backend.

Choice Sources

In all the examples so far the list of choices has been a literal list of values. That’s useful, but it’s also useful to have values that can change at runtime. In order to do that you need to provide choices with instructions on how to populate the choice list instead of the list itself.

In all cases the result of the choices operation must be a valid choices list.

URL

Specifying a URL will tell the browser to load choices using an HTTP GET request. You can use type 'url' if using dictionary configuration or just pass the URL as a string:

Choices URL example

@parameter(key="p1", choices='https://test.com/p1.json')
@parameter(key="p2", choices={"type": "url",
                              "value": 'https://test.com/p2.json'})
def format(self, p1, p2):
    ...

Be aware that the user’s browser will be making this request. So if the Beer Garden UI is being accessed at a secure (https) address then a request to a non-secure (http) URL will likely fail due to mixed-content restrictions.

Command

Specifying a command will load choices by making a request to the current system. You can use type 'command' if using dictionary configuration or just pass the command as a string. If you’re not using choice parameters (more on those in a minute) you can omit the parenthesis for brevity.

Choices Command example

@parameter(key="p1", choices="get_choices()")
@parameter(key="p2", choices={"type": "command",
                              "value": "get_choices"})
def format(self, p1, p2):
    ...

@command
def get_choices(self):
    return [
        {"text": "The best", "value": "json"},
        {"text": "The worst", "value": "xml"}
    ]

Currently you must use a command from the same system (this restriction will be removed in a future release - see issue 269).

Choice parameters

It’s often useful to have the choices for one parameter depend on the current value of another. To do that you can use choice parameters.

To create a reference on another parameter enclose its key in ${}. How the parameter is passed depends on what choice source is being used.

When initializing the command creation page, BeerGarden will attempt to update all dependencies for choice parameters at once. If the dependent parameters are defined in such a way that causes side effects inside the command (for example, if A is a choice parameter that depends on B and C, but updating C changes an internal value A and B need), this could lead to unintended consequences or destructive behavior during command load.

For 'command' types the parameter will be passed as an argument to the command. For example, suppose you have two parameters: day_type and day_of_week. You’d like the choices for day_of_week to depend on what the user has selected for day_type:

Choices Command Parameter example

@command
def get_days(self, type):
    if type == "Weekday":
        return ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
    elif type == "Weekend":
        return ["Saturday", "Sunday"]
    else:
      raise Exception("Huh?")

@parameter(key="day_type", choices=["Weekday", "Weekend"])
@parameter(key="day_of_week", choices="get_days(type=${day_type})")
def my_command(self, day_type, day_of_week):
    do_something(day_of_week)
    return "All done!"

For 'url' types the choice parameter should be used as a query parameter:

Choices URL Parameter example

@parameter(key="day_type", choices=["Weekday", "Weekend"])
@parameter(key="day_of_week",
           choices="https://getthedays.com?type=${day_type}")
def my_command(self, day_type, day_of_week):
    do_something(day_of_week)
    return "All done!"

Choice parameters also enable using a static choices dictionary with one parameter used as the dictionary key. To do this use type static and pass the dictionary as the value. Since we can construct the dictionary before defining the command we can rework the day_of_week example to look like this:

Choices Dictionary example

day_dict = {
    "Weekday": ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"],
    "Weekend": ["Saturday", "Sunday"]
}

@parameter(key="day_type", choices=["Weekday", "Weekend"])
@parameter(key="day_of_week", choices={'type': 'static',
                                       'value': day_dict,
                                       'key_reference': '${day_type}'})
def my_command(self, day_type, day_of_week):
    do_something(day_of_week)
    return "All done!"

When using a choices dictionary the None key can be used to specify the allowed values when the reference key is null. For example, if we wanted to modify the day_of_week example to additionally allow any day to be selected if day_type was null we could do this:

Choices Dictionary with None example

day_dict = {
    "Weekday": ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"],
    "Weekend": ["Saturday", "Sunday"],
    None: ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday",
           "Saturday", "Sunday"]
}

@parameter(key="day_type", choices=["Weekday", "Weekend"],
           nullable=True)
@parameter(key="day_of_week", choices={'type': 'static',
                                       'value': day_dict,
                                       'key_reference': '${day_type}'})
def my_command(self, day_type, day_of_week):
    do_something(day_of_week)
    return "All done!"

Is kwarg argument

The is_kwarg argument allows you to name a keyword argument that is otherwise unspecified. This is useful if you take keyword args, but want to call out the normal use-case ones more explicitly while still being compatible to other python libraries calling you.

Is kwarg argument example

@parameter(key="foo", is_kwarg=True)
def do_something(self, **kwarg):
    foo = kwarg.pop("foo")
    print(foo)

Model argument

The model argument allows you to specify some structure for a complicated object. Have a look at the following for an example of how to use the model field.

Model argument example

from brewtils.models import Parameter
class Person(object):

  name = Parameter(key="name",
                   type="String",
                   description="Person's name")
  age = Parameter(key="age",
                  type="Integer",
                  description="Person's age")

class ExampleClient(object):

    @parameter(key="person", model=Person)
    def greet(self, person):
        print("Hello %s" % person.name)

It is assumed that if you have a model, that the type is "Dictionary"

Nullable argument

The nullable argument allows you to specify if the parameter can be null. If the argument is allowed to be null, then you must tell us this is possible. The default is assuming that parameters cannot be null.

If there is a default value for a parameter, then nullable is set to True.

Nullable argument example

@parameter(key="foo", nullable=True))
def do_something(self, foo):
    if foo is None:
        print("That's ok!")
    else:
        print("That's ok too!")

Maximum argument

The maximum argument allows you to specify the maximum value for a parameter. This meaning changes based on the type and whether or not the multi flag is enabled. If the multi flag is enabled, then maximum is referring to the list length maximum. Otherwise, if type is integer, it will compare the value of the parameter to the maximum. Otherwise if the type is a string, it will ensure the length of the string is within bounds.

Maximum argument example

@parameter(key="foo", type="String", maximum=1)
@parameter(key="bar", type="Integer", maximum=1)
@parameter(key="bazs", type="String", maximum=1)
def do_something(self, foo, bar, bazs):
    # guarantees that foo is 1 character at most
    # guarantees that bar is no more than 1
    # guarantees that bazs is no more than 1 item long
    print(foo)
    print(bar)
    print(bazs)

Minimum argument

The minimum argument allows you to specify the minimum value for a parameter. This meaning changes based on the type and whether or not the multi flag is enabled. If the multi flag is enabled, then minimum is referring to the list length minimum. Otherwise, if type is integer, it will compare the value of the parameter to the minimum. Otherwise if the type is a string, it will ensure the length of the string is within bounds.

Minimum argument example

@parameter(key="foo", type="String", minimum=1)
@parameter(key="bar", type="Integer", minimum=1)
@parameter(key="bazs", type="String", minimum=1)
def do_something(self, foo, bar, bazs):
    # guarantees that foo is at least 1 character
    # guarantees that bar is no less than 1
    # guarantees that bazs is no less than 1 item long
    print(foo)
    print(bar)
    print(bazs)

Regex argument

The regex argument allows you to specify a regex that the parameter must pass in order to be considered valid.

Regex argument example

@parameter(key="ip", regex=r'^\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}$')
def do_something(self, ipv4):
    print("This is a valid IPv4: %s" % ipv4)

Form Input Type Argument

The form_input_type field allows you control over how Beer Garden renders the text-field. This is useful if you have some string field that is actually quite long. Currently the only supported type is textarea.

Input Form Type argument example

@parameter(key="comment", type="String", form_input_type="textarea")
def do_something(self, comment):
    print("This is a long comment: %s" % comment)

Customizing Command Form

The ability to customize the command form is a deprecated feature that will be removed in the relatively near future. For now, the documentation regarding this feature is still available here.

External Logging

Starting in Beer Garden 2.1.0, it is possible to tell your plugins how to log from the Beer Garden application itself. Beer Garden provides a new api (/api/v1/config/logging) which will respond with a logging configuration that plugins can optionally use. Checkout our Swagger documentation for the complete details of this new endpoint.

This allows you to do one-time configuration of a logger in Beer Garden configuration files and propagate that logging configuration to all of your plugins. To use it, you simply add the following to your entry point.

from brewtils.log import setup_logger

# Your client definition Here

if __name__ == "__main__":
    setup_logger(
        bg_host='localhost',
        bg_port=2337,
        system_name='my_name',
        ca_cert=None,
        client_cert=None,
        ssl_enabled=None,
    )
    # Init your plugin as normal.

This tells Beer Garden to setup a root logger based on what is returned from the endpoint at api/v1/config/logging. Checkout the configuration section for more information on how to configure this. This is mostly useful for remote plugins.

Python Plugin Guide (Remote)

Prerequisites

Hello World!

Write the code

Run the code

Use the code

Stop the code

Exception Handling

Making your plugin more descriptive

Adding a command description

Describing a parameter

Key argument

Type argument

Multi argument

Display name argument

Optional argument

Default argument

Description argument

Choices argument

Basic Usage

Additional Configuration

Choices Type

Display

Strictness

Choice Sources

URL

Command

Choice parameters

Is kwarg argument

Model argument

Nullable argument

Maximum argument

Minimum argument

Regex argument

Form Input Type Argument

Customizing Command Form

External Logging