Getting started with ppacer

Intro

To begin, we’ll set up new Go project, install ppacer and run hello world example.

Installing ppacer

mkdir ppacer-demo && cd ppacer-demo
go mod init ppacerDemo
go get github.com/ppacer/core@latest
go get github.com/ppacer/tasks@latest
go get github.com/ppacer/ui@latest

mkdir ppacer-demo
cd ppacer-demo

go mod init ppacerDemo
go get github.com/ppacer/core@latest
go get github.com/ppacer/tasks@latest
go get github.com/ppacer/ui@latest

Hello World

Now, let’s proceed to initiate the ppacer with a single DAG. Start by creating a file named main.go with the following content:

package main

import (
    "context"
    "time"

    "github.com/ppacer/core"
    "github.com/ppacer/core/dag"
    "github.com/ppacer/core/dag/schedule"
    "github.com/ppacer/tasks"
    "github.com/ppacer/ui"
)

const (
    schedulerPort = 9321
    uiPort        = 9322
)

func main() {
    ctx := context.Background()

    dags := dag.Registry{}
    dags.Add(printDAG("hello_world_dag"))

    go func() {
        ui.DefaultStarted(schedulerPort, uiPort)
    }()
    core.DefaultStarted(ctx, dags, schedulerPort)
}

func printDAG(dagId string) dag.Dag {
    //         t21
    //       /
    // start
    //       \
    //         t22 --> finish
    start := dag.NewNode(tasks.NewPrintTask("start", "hello"))
    t21 := dag.NewNode(tasks.NewPrintTask("t21", "foo"))
    t22 := dag.NewNode(tasks.NewPrintTask("t22", "bar"))
    finish := dag.NewNode(tasks.NewPrintTask("finish", "I'm done!"))

    start.Next(t21)
    start.Next(t22)
    t22.Next(finish)

    startTs := time.Date(2024, time.March, 11, 12, 0, 0, 0, time.Local)
    schedule := schedule.NewFixed(startTs, 10*time.Second)

    printDag := dag.New(dag.Id(dagId)).
        AddSchedule(&schedule).
        AddRoot(start).
        Done()
    return printDag
}

Now we can compile and run our program.

go build
./ppacerDemo

go build
.\ppacerDemo.exe

Upon running, you should see a bunch of INFO logs from ppacer Scheduler. Please feel free to skip those logs and go straight to the UI at http://localhost:9322.

If you want a less noisy stdout, you can increase the log severity level using an environment variable:

PPACER_LOG_LEVEL=WARN ./ppacerDemo

$env:PPACER_LOG_LEVEL = "WARN"
.\ppacerDemo.exe

Explanations

So what actually happened in our program? On high level we defined a DAG which prints messages in particular order and runs each 10 seconds. Let’s break down the main.go file.

Import the Go standard and ppacer packages:

import (
    "context"
    "time"

    "github.com/ppacer/core"
    "github.com/ppacer/core/dag"
    "github.com/ppacer/core/dag/schedule"
    "github.com/ppacer/tasks"
    "github.com/ppacer/ui"
)

Define constants for ppacer Scheduler and UI ports:

const (
    schedulerPort = 9321
    uiPort        = 9322
)

The main function in main package is the program entry point in Go.
Define the required context for the ppacer Scheduler:
```
ctx := context.Background()
```
Initialize the DAG registry and add new DAG from printDAG function:
```
dags := dag.Registry{}
dags.Add(printDAG("hello_world_dag"))
```
Spin off the ppacer UI in a separate goroutine (so it can run in parallel to the Scheduler)
```
go func() {
    ui.DefaultStarted(schedulerPort, uiPort)
}()
```
Start the ppacer Scheduler (also in the form of an HTTP server) with the default configuration for given context, DAG registry and port:
```
core.DefaultStarted(ctx, dags, schedulerPort)
```
The printDAG function defines a DAG for printing messages in particular order. Details on DAGs, Tasks and schedules can be found further in the documentation.

Complete example

The whole source code for above example can be found in here: github.com/ppacer/examples.