Creating a Plugin

To create Actions and Flows for your organization, you need to start by creating a plugin.

Plugins are delivered in a Docker image. When installed, a Kubernetes pod is launched where the Actions run inside. Plugins created with the DeltaFi Action Kit will automatically register with the DeltaFi Core at startup. Registration identifies all Actions, Action Parameter classes, and general information about the plugin. Typically, a plugin includes one or more Flows which use the custom Actions and Flow Variables, but they are both optional. Flows and Flow Variables are also included in the Plugin registration.

A plugin project can be created in a variety of ways. The simplest way to start is using a single Git repository to host a single Plugin, which builds with Gradle. DeltaFi provides examples for this in Java, Python, Go, and C++. For Java, DeltaFi provides a custom Gradle plugin to facilitate the Docker build and Plugin structure. The Python structure requires a few extra files. The Go structure uses standard Go modules and a multi-stage Docker build.

Java

The overall Java structure is shown below and requires downloading the deltafi-action-kit JAR from a Gitlab/Maven repository.

myplugin/
| - src/main/java/...
| - src/main/resources/flows/
| - build.gradle
| - gradle.properties
| - settings.gradle

The src directory is where your Actions will be developed using normal Java conventions (main/java/..., main/resources, test/java/..., test/resources, etc).

Gradle Files

Start with a settings.gradle, where we'll set up access to Maven repositories.

groovy

pluginManagement {
    repositories {
        mavenLocal()
        mavenCentral()
        gradlePluginPortal()
        maven {
            url deltafiMavenRepo
            name "GitLab"
            credentials(HttpHeaderCredentials) {
                name = gitLabTokenType
                value = gitLabToken
            }
            authentication {
                header(HttpHeaderAuthentication)
            }
        }
    }
}

dependencyResolutionManagement {
    repositories {
        mavenLocal()
        mavenCentral()
        maven {
            url deltafiMavenRepo
            name "GitLab"
            credentials(HttpHeaderCredentials) {
                name = gitLabTokenType
                value = gitLabToken
            }
            authentication {
                header(HttpHeaderAuthentication)
            }
        }
    }
}

Next we'll use the gradle.properties to store a few variables. Set deltafiVersion to your target action-kit version.

groovy

org.gradle.jvmargs=-Xmx1024M
org.gradle.logging.level=INFO
systemProp.org.gradle.internal.http.socketTimeout=120000
systemProp.org.gradle.internal.http.connectionTimeout=120000

deltafiVersion=0.100.0

deltafiMavenRepo=https://gitlab.com/api/v4/projects/25005502/packages/maven
projectMavenRepo=https://gitlab.com/api/v4/projects/34705336/packages/maven

localDockerRegistry=localhost:5000

Finally, you need some special setup in your build.gradle to create the plugin. By using the latest org.deltafi.plugin-convention your Gradle tasks can generate a Spring Boot Docker image which automatically has the correct hooks to register your Plugin with DeltaFi. A local Dockerfile is not necessary.

groovy

plugins {
    id "org.deltafi.plugin-convention" version "${deltafiVersion}"
}

group 'org.myorg.plugingroup'

ext.pluginDescription = 'My plugin actions'

Python

The Python action kit for DeltaFi is published on PyPi. A project structure for a DeltaFi Python Plugin is shown below:

build.gradle
DockerFile
gradle.properties
settings.gradle
src/flows/
src/plugin.py
src/actions/...
src/pyproject.toml:

A DeltaFi Plugin can easily be written and built using a Gradle and Poetry framework. A set of skeleton files are provided below.

Skeleton Files

Start with a build.gradle that includes the sections below. It needs the docker plugin and associated assembly properties, the group variable, and poetry commands.

groovy

plugins {
  id 'org.deltafi.git-version' version "2.0.1"
  id "com.palantir.docker" version "${palantirDockerVersion}"
}

group 'org.deltafi.python-poc'

task clean(type: Delete) {
  delete 'src/dist'
}

task test {}

task replaceDeltafiVersion(type: Exec) {
  def deltafiVersion = project.deltafiVersion
  def tokens = deltafiVersion.tokenize('.')
  def patchfull = tokens.get(2)
  def patch = patchfull.tokenize('-').get(0)

  if (deltafiVersion.contains("SNAPSHOT")) {
    deltafiVersion = ">=${tokens.get(0)}.${tokens.get(1)}.${patch}rc0"
  } else {
    deltafiVersion = "==${tokens.get(0)}.${tokens.get(1)}.${tokens.get(2)}"
  }
  commandLine 'sed', "s/DELTAFI_VERSION/${deltafiVersion}/g", 'src/pyproject.toml.template'
  standardOutput new FileOutputStream('src/pyproject.toml')
}

task setupPoetry(type: Exec) {
  commandLine 'pip3', '-q', 'install', 'poetry'
}

task assemble(type: Exec) {
  dependsOn replaceDeltafiVersion, setupPoetry

  workingDir 'src'
  commandLine 'poetry', 'lock'
}

docker {
  dependsOn assemble

  name "${project.name}:${project.version}"
  tag 'local', "${localDockerRegistry}/${project.name}:latest"
  def args = ['PROJECT_GROUP': group, 'PROJECT_NAME': project.name, 'PROJECT_VERSION': project.version]
  if (project.hasProperty('gitLabToken')) {
    args['GITLAB_TOKEN'] = gitLabToken
    args['GITLAB_USER'] = "__token__"
  }
  buildArgs(args)
  copySpec.from('src').include('**').into('src')
}

A Dockerfile must be created to create the Python Plugin image. To satisfy the DeltaFi Python dependencies, the base image must use a minimum Python version of 3.7. The PROJECT variables are needed for proper registration with DeltaFi. The entrypoint for the image is typically plugin.py, but may be changed.

FROM python:3.7-slim

ENV PYTHONDONTWRITEBYTECODE 1
ENV PYTHONUNBUFFERED 1

WORKDIR /code

COPY src/. /code/
RUN pip install poetry && poetry config virtualenvs.create false

RUN poetry install

ARG PROJECT_NAME
ARG PROJECT_GROUP
ARG PROJECT_VERSION

ENV PROJECT_NAME $PROJECT_NAME
ENV PROJECT_GROUP $PROJECT_GROUP
ENV PROJECT_VERSION $PROJECT_VERSION

ENTRYPOINT [ "python", "/code/plugin.py" ]

Create the gradle.properties with the settings below.

groovy

org.gradle.jvmargs=-Xmx1024M
org.gradle.logging.level=INFO
systemProp.org.gradle.internal.http.socketTimeout=120000
systemProp.org.gradle.internal.http.connectionTimeout=120000

palantirDockerVersion=0.22.1
deltafiVersion=0.100.0
localDockerRegistry=localhost:5000

Poetry

Poetry is used to install the plugin when building the Docker image. Building and installing your Plugin with Poetry requires a src/pyproject.toml file. Use the example below. Make sure the version of deltafi dependency is compatible with your running DeltaFi Core.

[tool.poetry]
name = "myplugin-package-name"
version = "0.1.0"
description = "This is my package description"
authors = ["Somebody <somebody@domain.com>"]
readme = "README.md"
packages = []

[tool.poetry.dependencies]
python = "^3.7"
deltafi = "0.100.0"

[build-system]
requires = ["poetry-core"]
build-backend = "poetry.core.masonry.api"

Python Entrypoint

An entrypoint Python script is needed to start the Plugin when the Docker container is deployed. The entrypoint script must identify the Actions to the Plugin class and call the run() method. See the following src/plugin.py example. Update the Action name and module to match your first Action.

python

#!/usr/bin/env python3

from actions.transform_action import MyTransformAction
from deltafi.plugin import Plugin

Plugin([MyTransformAction],
    "This is the description of the demo plugin").run()

Go

Beta

The Go action kit is currently in beta. Interfaces may change in future releases.

The Go action kit is published as a Go module. A project structure for a DeltaFi Go Plugin is shown below:

myplugin/
├── go.mod
├── go.sum
├── main.go
├── plugin.yaml
├── Makefile
├── Dockerfile
├── actions/
│   ├── my_transform_action.go
│   ├── my_transform_action_params.go
│   ├── my_transform_action_params.json   (optional, see "Schema round-trip")
│   ├── my_transform_action.yaml
│   └── my_transform_action_test.go
├── flows/
│   └── my-transform.json
└── integration/
    └── basic-test.json

Each action ships in two Go files:

<name>_action.go — the action struct, init() registration, and the action method
<name>_action_params.go — the typed *Params struct only

Splitting the params struct into a sibling file keeps the action focused on logic and gives the schema round-trip tooling (described below) a deterministic location to read from and write to.

Go Module

Start with a go.mod that imports the action kit:

module gitlab.com/deltafi/deltafi/my-plugin

go 1.26

require gitlab.com/deltafi/deltafi/deltafi-go-action-kit/v2 v2.52.3

Go Entrypoint

The entrypoint registers actions and starts the plugin. Actions self-register via init() functions, so they only need a blank import. The RunPlugin function handles all plugin lifecycle boilerplate.

package main

import (
    actionkit "gitlab.com/deltafi/deltafi/deltafi-go-action-kit/v2"
    _ "gitlab.com/deltafi/deltafi/my-plugin/actions"
)

func main() {
    actionkit.RunPlugin()
}

Plugin identity lives in plugin.yaml at the repo root:

yaml

groupId: org.myorg
artifactId: my-plugin
domain: org.myorg.my-plugin
description: My DeltaFi plugin

The Makefile extracts these fields from plugin.yaml and passes them to the Docker build, which stamps them into the binary via -ldflags -X so production binaries are self-contained. When running locally via go run ., the kit falls back to reading ./plugin.yaml directly. Version is supplied at link time via -X gitlab.com/deltafi/deltafi/deltafi-go-action-kit/v2.PluginVersion=<version> and defaults to 0.0.0-dev.

Parameters and schema round-trip

The kit reads the following struct tags on parameter fields when it generates the JSON Schema that core uses to render the DeltaFi UI:

Tag	Effect
`json:"name"`	parameter name in the UI
`description:"..."`	human-readable description
`default:"..."`	default value (string form; coerced to the field type)
`enum:"a,b,c"`	allowed values (renders as a dropdown)
`required:"true"`	marks the parameter as required
`minimum:"0"` / `maximum:"100"`	numeric bounds

Supported field types: Go primitives (bool, int, string, float64), slices, string-keyed maps, pointers to named structs declared in the same params file, and the kit's actionkit.DataSize and actionkit.EnvVar helpers.

Two Make targets convert between the Go source and a standalone JSON Schema file:

make jsonFromParams   # writes actions/<name>_action_params.json from each _params.go
make paramsFromJson   # writes actions/<name>_action_params.go   from each _params.json

Both targets invoke gitlab.com/deltafi/deltafi/deltafi-go-action-kit/v2/cmd/actionkit-schemagen, a pure file-by-file AST tool — no plugin compilation required. jsonFromParams produces schemas that are byte-for-byte identical to what the kit sends to core during plugin registration (the AST tool reuses the kit's actionkit.GenerateSchema logic). paramsFromJson regenerates the Go source from a schema; the output is canonical (fields alphabetize, comments drop, slice-of-struct fields come back as slice-of-pointer-to-struct) but functionally equivalent.

Either direction is the source of truth; pick the workflow that fits the team. Round-tripping is idempotent from the first JSON onward.

Dockerfile

Go plugins use a multi-stage Docker build:

dockerfile

FROM golang:1.26-alpine AS builder

WORKDIR /build
COPY deltafi-go-action-kit/go.mod deltafi-go-action-kit/go.sum ./deltafi-go-action-kit/
COPY my-plugin/go.mod my-plugin/go.sum ./my-plugin/

WORKDIR /build/my-plugin
RUN go mod download -x

WORKDIR /build
COPY deltafi-go-action-kit/ ./deltafi-go-action-kit/
COPY my-plugin/ ./my-plugin/

WORKDIR /build/my-plugin
ARG VERSION=0.0.0-dev
ARG DESCRIPTION=My DeltaFi plugin
RUN CGO_ENABLED=0 GOOS=linux go build -ldflags "\
  -X main.version=${VERSION} \
  -X 'main.description=${DESCRIPTION}'" \
  -o my-plugin .

FROM alpine:3.23
RUN apk --no-cache add ca-certificates
WORKDIR /app
COPY --from=builder /build/my-plugin/my-plugin deltafi-plugin
COPY --from=builder /build/my-plugin/flows ./flows
RUN chmod +x deltafi-plugin
ENTRYPOINT ["/app/deltafi-plugin"]

Makefile

A Makefile simplifies common tasks:

makefile

VERSION ?= $(shell git describe --tags --always --dirty)

.PHONY: build test vet

build:
	go build -ldflags "-X main.version=$(VERSION)" -o my-plugin .

test:
	go test ./...

vet:
	go vet ./...

C++

Beta

The C++ action kit is currently in beta. Interfaces may change in future releases.

The C++ action kit is a header-only library. A project structure for a DeltaFi C++ Plugin is shown below:

myplugin/
├── CMakeLists.txt
├── Makefile
├── Dockerfile
├── main.cpp
├── actions/
│   └── transform.hpp
├── suppliers/           # optional lookup-table suppliers
├── lookup-tables/       # optional shared data files served by suppliers
├── flows/
│   └── my-transform.json
└── integration/
    └── basic-test.json

The deltafi-cpp-hello-world reference plugin exercises the full surface, including a streaming flow (DeleteContent → LoremIpsum → Capitalize) whose actions demonstrate bounded-memory writer-callback and load-reader streaming, a streaming egress that scans for a marker across read boundaries, and lookup suppliers backed by shared lookup-tables/ data files.

CMake

Start with a CMakeLists.txt that imports the action kit:

cmake

cmake_minimum_required(VERSION 3.20)
project(my_plugin VERSION 0.1.0 LANGUAGES CXX)

set(DELTAFI_ACTION_KIT_PATH "" CACHE PATH "Local path to deltafi-cpp-action-kit")

if(DELTAFI_ACTION_KIT_PATH)
    add_subdirectory(${DELTAFI_ACTION_KIT_PATH}
                     ${CMAKE_CURRENT_BINARY_DIR}/deltafi-cpp-action-kit)
else()
    include(FetchContent)
    FetchContent_Declare(deltafi_cpp_action_kit
        GIT_REPOSITORY https://gitlab.com/deltafi/deltafi.git
        GIT_TAG        main
        SOURCE_SUBDIR  deltafi-cpp-action-kit
    )
    FetchContent_MakeAvailable(deltafi_cpp_action_kit)
endif()

if(NOT DEFINED VERSION)
    set(VERSION "0.0.0-dev")
endif()

add_executable(my-plugin main.cpp)
target_link_libraries(my-plugin PRIVATE deltafi::action_kit)
target_compile_definitions(my-plugin PRIVATE VERSION="${VERSION}")
target_include_directories(my-plugin PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})

C++ Entrypoint

Actions self-register via DELTAFI_ACTION macros, so the entrypoint only needs to include action headers and use the DELTAFI_PLUGIN macro:

cpp

#include <deltafi/plugin>
#include "actions/transform.hpp"

DELTAFI_PLUGIN(
    "org.myorg",
    "my-plugin",
    "My DeltaFi C++ plugin",
    "org.myorg.my-plugin"
)

Dockerfile

C++ plugins use a multi-stage Docker build with a BUILD_FLAVOR arg that selects the libc:

glibc (default) — a dynamically-linked binary, built on debian:trixie-slim (g++-14 provides <format>, which the kit's spdlog needs) and shipped on the matching gcr.io/distroless/cc-debian13:nonroot. Preferred for its robust DNS/NSS, locale, and thread stacks.
musl — a fully-static binary, built on alpine:3.24 and shipped on gcr.io/distroless/static:nonroot. Smallest image, but with musl's DNS/NSS, locale, and 128 KiB thread-stack limits.

Build and runtime must share a libc version, so each flavor pairs a builder base with a matching runtime base and the two are selected together by BUILD_FLAVOR:

dockerfile

ARG BUILD_FLAVOR=glibc

FROM alpine:3.24 AS builder-musl
RUN apk add --no-cache cmake make ninja linux-headers g++ git openssl openssl-dev openssl-libs-static
ENV DELTAFI_CMAKE_LINK_FLAGS="-DCMAKE_EXE_LINKER_FLAGS=-static -DOPENSSL_USE_STATIC_LIBS=TRUE"

FROM debian:trixie-slim AS builder-glibc
RUN apt-get update && apt-get install -y --no-install-recommends \
        cmake ninja-build g++ git libssl-dev ca-certificates \
    && rm -rf /var/lib/apt/lists/*
ENV DELTAFI_CMAKE_LINK_FLAGS=""

FROM builder-${BUILD_FLAVOR} AS builder
WORKDIR /build
COPY deltafi-cpp-action-kit/ ./deltafi-cpp-action-kit/
COPY my-plugin/ ./my-plugin/
WORKDIR /build/my-plugin
ARG VERSION=0.0.0-dev
RUN cmake -B build -G Ninja -DCMAKE_BUILD_TYPE=Release \
    -DDELTAFI_ACTION_KIT_PATH=/build/deltafi-cpp-action-kit \
    -DVERSION=${VERSION} ${DELTAFI_CMAKE_LINK_FLAGS}
RUN cmake --build build

FROM gcr.io/distroless/static:nonroot AS runtime-musl
FROM gcr.io/distroless/cc-debian13:nonroot AS runtime-glibc

FROM runtime-${BUILD_FLAVOR}
COPY --from=builder /build/my-plugin/build/my-plugin /app/deltafi-plugin
COPY --from=builder /build/my-plugin/flows /app/flows
ENTRYPOINT ["/app/deltafi-plugin"]

Select a flavor through the Makefile's BUILD_FLAVOR flag (default glibc):

bash

make docker                    # glibc (default)
make docker BUILD_FLAVOR=musl  # static musl

Makefile

A Makefile simplifies common tasks:

makefile

VERSION ?= $(shell git describe --tags --always --dirty)

.PHONY: build test clean

build:
	cmake -B build -DVERSION=$(VERSION) -DDELTAFI_ACTION_KIT_PATH=../deltafi-cpp-action-kit
	cmake --build build

test: build
	ctest --test-dir build --output-on-failure

clean:
	rm -rf build

Flows

Flows may be defined for a Plugin. See Flows.

Lookup Tables

Lookup tables may be used by a Plugin. See Lookup Tables.

Testing Plugin Actions

Java actions can be tested with standard unit tests along with the helpers in the deltafi-action-kit-test dependency. Go actions use the test helpers built into the deltafi-go-action-kit package. C++ actions use the test helpers in the deltafi/testing.hpp header. See Action Unit Testing.

To test complete data flows end-to-end, use integration tests. Integration tests validate that your data sources, transforms, and data sinks work together correctly. See Integration Testing.

Creating a Plugin ​

Java ​

Gradle Files ​

Python ​

Skeleton Files ​

Poetry ​

Python Entrypoint ​

Go ​

Go Module ​

Go Entrypoint ​

Parameters and schema round-trip ​

Dockerfile ​

Makefile ​

C++ ​

CMake ​

C++ Entrypoint ​

Dockerfile ​

Makefile ​

Flows ​

Lookup Tables ​

Testing Plugin Actions ​

Creating a Plugin

Java

Gradle Files

Python

Skeleton Files

Poetry

Python Entrypoint

Go

Go Module

Go Entrypoint

Parameters and schema round-trip

Dockerfile

Makefile

C++

CMake

C++ Entrypoint

Dockerfile

Makefile

Flows

Lookup Tables

Testing Plugin Actions