Deploying and managing Pulsar Functions Preview

A guide to Pulsar Functions from an operational perspective

At the moment, there are two deployment modes available for Pulsar Functions:

Mode Description
Local run mode The function runs in your local environment, for example on your laptop
Cluster mode The function runs inside of your Pulsar cluster, on the same machines as your Pulsar brokers

Contributing new deployment modes

The Pulsar Functions feature was designed, however, with extensibility in mind. Other deployment options will be available in the future. If you’d like to add a new deployment option, we recommend getting in touch with the Pulsar developer community at


In order to deploy and manage Pulsar Functions, you need to have a Pulsar cluster running. There are several options for this:

If you’re running a non-standalone cluster, you’ll need to obtain the service URL for the cluster. How you obtain the service URL will depend on how you deployed your Pulsar cluster.

Command-line interface

Pulsar Functions are deployed and managed using the pulsar-admin functions interface, which contains commands such as create for deploying functions in cluster mode, trigger for triggering functions, list for listing deployed functions, and several others.

Fully Qualified Function Name (FQFN)

Each Pulsar Function has a Fully Qualified Function Name (FQFN) that consists of three elements: the function’s tenant, namespace, and function name. FQFN’s look like this:


FQFNs enable you to, for example, create multiple functions with the same name provided that they’re in different namespaces.

Default arguments

When managing Pulsar Functions, you’ll need to specify a variety of information about those functions, including tenant, namespace, input and output topics, etc. There are some parameters, however, that have default values that will be supplied if omitted. The table below lists the defaults:

Parameter Default
Function name Whichever value is specified for the class name (minus org, library, etc.). The flag --className org.example.MyFunction, for example, would give the function a name of MyFunction.
Tenant Derived from the input topics’ names. If the input topics are under the marketing tenant—i.e. the topic names have the form persistent://marketing/{namespace}/{topicName}—then the tenant will be marketing.
Namespace Derived from the input topics’ names. If the input topics are under the asia namespace under the marketing tenant—i.e. the topic names have the form persistent://marketing/asia/{topicName}, then the namespace will be asia.
Output topic {input topic}-{function name}-output. A function with an input topic name of incoming and a function name of exclamation, for example, would have an output topic of incoming-exclamation-output.
Subscription type For at-least-once and at-most-once processing guarantees, the SHARED is applied by default; for effectively-once guarantees, FAILOVER is applied
Processing guarantees ATLEAST_ONCE
Pulsar service URL pulsar://localhost:6650

Example use of defaults

Take this create command:

$ bin/pulsar-admin functions create \
  --jar my-pulsar-functions.jar \
  --className org.example.MyFunction \
  --inputs my-function-input-topic1,my-function-input-topic2

The created function would have default values supplied for the function name (MyFunction), tenant (public), namespace (default), subscription type (SHARED), processing guarantees (ATLEAST_ONCE), and Pulsar service URL (pulsar://localhost:6650).

Local run mode

If you run a Pulsar Function in local run mode, it will run on the machine from which the command is run (this could be your laptop, an AWS EC2 instance, etc.). Here’s an example localrun command:

$ bin/pulsar-admin functions localrun \
  --py \
  --className myfunc.SomeFunction \
  --inputs persistent://public/default/input-1 \
  --output persistent://public/default/output-1

By default, the function will connect to a Pulsar cluster running on the same machine, via a local broker service URL of pulsar://localhost:6650. If you’d like to use local run mode to run a function but connect it to a non-local Pulsar cluster, you can specify a different broker URL using the --brokerServiceUrl flag. Here’s an example:

$ bin/pulsar-admin functions localrun \
  --brokerServiceUrl pulsar://my-cluster-host:6650 \
  # Other function parameters

Cluster mode

When you run a Pulsar Function in cluster mode, the function code will be uploaded to a Pulsar broker and run alongside the broker rather than in your local environment. You can run a function in cluster mode using the create command. Here’s an example:

$ bin/pulsar-admin functions create \
  --py \
  --className myfunc.SomeFunction \
  --inputs persistent://public/default/input-1 \
  --output persistent://public/default/output-1

Updating cluster mode functions

You can use the update command to update a Pulsar Function running in cluster mode. This command, for example, would update the function created in the section above:

$ bin/pulsar-admin functions update \
  --py \
  --className myfunc.SomeFunction \
  --inputs persistent://public/default/new-input-topic \
  --output persistent://public/default/new-output-topic


Pulsar Functions run as processes called instances. When you run a Pulsar Function, it runs as a single instance by default (and in local run mode you can only run a single instance of a function).

You can also specify the parallelism of a function, i.e. the number of instances to run, when you create the function. You can set the parallelism factor using the --parallelism flag of the create command. Here’s an example:

$ bin/pulsar-admin functions create \
  --parallelism 3 \
  # Other function info

You can adjust the parallelism of an already created function using the update interface.

$ bin/pulsar-admin functions update \
  --parallelism 5 \
  # Other function

If you’re specifying a function’s configuration via YAML, use the parallelism parameter. Here’s an example config file:

# function-config.yaml
parallelism: 3
- persistent://public/default/input-1
output: persistent://public/default/output-1
# other parameters

And here’s the corresponding update command:

$ bin/pulsar-admin functions update \
  --functionConfigFile function-config.yaml

Function instance resources

When you run Pulsar Functions in cluster run mode, you can specify the resources that are assigned to each function instance:

Resource Specified as… Runtimes
CPU The number of cores Docker (coming soon)
RAM The number of bytes Process, Docker
Disk space The number of bytes Docker

Here’s an example function creation command that allocates 8 cores, 8 GB of RAM, and 10 GB of disk space to a function:

$ bin/pulsar-admin functions create \
  --jar target/my-functions.jar \
  --className org.example.functions.MyFunction \
  --cpu 8 \
  --ram 8589934592 \
  --disk 10737418240

Resources are per instance

The resources that you apply to a given Pulsar Function are applied to each instance of the function. If you apply 8 GB of RAM to a function with a paralellism of 5, for example, then you are applying 40 GB of RAM total for the function. You should always make sure to factor paralellism—i.e. the number of instances—into your resource calculations.

Triggering Pulsar Functions

If a Pulsar Function is running in cluster mode, you can trigger it at any time using the command line. Triggering a function means that you send a message with a specific value to the function and get the function’s output (if any) via the command line.

Triggering a function is ultimately no different from invoking a function by producing a message on one of the function’s input topics. The pulsar-admin functions trigger command is essentially a convenient mechanism for sending messages to functions without needing to use the pulsar-client tool or a language-specific client library.

To show an example of function triggering, let’s start with a simple Python function that returns a simple string based on the input:

def process(input):
    return "This function has been triggered with a value of {0}".format(input)

Let’s run that function in local run mode:

$ bin/pulsar-admin functions create \
  --tenant public \
  --namespace default \
  --name myfunc \
  --py \
  --className myfunc \
  --inputs persistent://public/default/in \
  --output persistent://public/default/out

Now let’s make a consumer listen on the output topic for messages coming from the myfunc function using the pulsar-client consume command:

$ bin/pulsar-client consume persistent://public/default/out \
  --subscription-name my-subscription
  --num-messages 0 # Listen indefinitely

Now let’s trigger that function:

$ bin/pulsar-admin functions trigger \
  --tenant public \
  --namespace default \
  --name myfunc \
  --triggerValue "hello world"

The consumer listening on the output topic should then produce this in its logs:

----- got message -----
This function has been triggered with a value of hello world

Topic info not required

In the trigger command above, you may have noticed that you only need to specify basic information about the function (tenant, namespace, and name). To trigger the function, you didn’t need to know the function’s input topic(s).