A simple but powerful DAG scheduler and dashboard, written in Go.
Use it if:
- you need a directed acyclic graph (DAG) scheduler like Apache Airflow, but without the complexity.
- you have a variety of clusters or services performing heavy computations and you want something small and light to orchestrate them.
- you want a monitoring dashboard.
- you want the easiest possible deployment with a single binary or container, saving you time. Volume mounts etc are too much headache.
- you want it to run on a single tiny VM, saving on cloud costs.
- you want to choose your storage technology--embedded, Postgres, Redis, S3, DynamoDB or something else.
- you prefer to define your DAGs with code rather than configuration files. This approach can make it easier to manage complex DAGs.
Don't use it if:
- you need to queue a huge number of tasks. Goflow is not tested at massive scale and does not support horizontal scaling.
docker run -p 8181:8181 ghcr.io/fieldryand/goflow-example:latestCheck out the dashboard at localhost:8181.
In a fresh project directory:
go mod init # create a new module
go get github.com/fieldryand/goflow/v2 # install dependenciesCreate a file main.go with contents:
package main
import "github.com/fieldryand/goflow/v2"
func main() {
options := goflow.Options{
UIPath: "ui/",
ShowExamples: true,
WithSeconds: true,
}
gf := goflow.New(options)
gf.Use(goflow.DefaultLogger())
gf.Run(":8181")
}Download and untar the dashboard:
wget https://github.com/fieldryand/goflow/releases/latest/download/goflow-ui.tar.gz
tar -xvzf goflow-ui.tar.gz
rm goflow-ui.tar.gzNow run the application with go run main.go and see it in the browser at localhost:8181.
First a few definitions.
Job: A Goflow workflow is called aJob. Jobs can be scheduled using cron syntax.Task: Each job consists of one or more tasks organized into a dependency graph. A task can be run under certain conditions; by default, a task runs when all of its dependencies finish successfully.- Concurrency: Jobs and tasks execute concurrently.
Operator: AnOperatordefines the work done by aTask. Goflow comes with a handful of basic operators, and implementing your ownOperatoris straightforward.- Retries: You can allow a
Taska given number of retry attempts. Goflow comes with two retry strategies,ConstantDelayandExponentialBackoff. - Streaming: Goflow uses server-sent events to stream the status of jobs and tasks to the dashboard in real time.
Let's start by creating a function that returns a job called my-job. There is a single task in this job that sleeps for one second.
package main
import (
"errors"
"github.com/fieldryand/goflow/v2"
)
func myJob() *goflow.Job {
j := &goflow.Job{Name: "my-job", Schedule: "* * * * *", Active: true}
j.Add(&goflow.Task{
Name: "sleep-for-one-second",
Operator: goflow.Command{Cmd: "sleep", Args: []string{"1"}},
})
return j
}By setting Active: true, we are telling Goflow to apply the provided cron schedule for this job when the application starts.
Job scheduling can be activated and deactivated from the dashboard.
A custom Operator needs to implement the Run method. Here's an example of an operator that adds two positive numbers.
type PositiveAddition struct{ a, b int }
func (o PositiveAddition) Run() (interface{}, error) {
if o.a < 0 || o.b < 0 {
return 0, errors.New("Can't add negative numbers")
}
result := o.a + o.b
return result, nil
}Let's add a retry strategy to the sleep-for-one-second task:
func myJob() *goflow.Job {
j := &goflow.Job{Name: "my-job", Schedule: "* * * * *"}
j.Add(&goflow.Task{
Name: "sleep-for-one-second",
Operator: goflow.Command{Cmd: "sleep", Args: []string{"1"}},
Retries: 5,
RetryDelay: goflow.ConstantDelay{Period: 1},
})
return j
}Instead of ConstantDelay, we could also use ExponentialBackoff (see https://en.wikipedia.org/wiki/Exponential_backoff).
A job can define a directed acyclic graph (DAG) of independent and dependent tasks. Let's use the SetDownstream method to
define two tasks that are dependent on sleep-for-one-second. The tasks will use the PositiveAddition operator we defined earlier,
as well as a new operator provided by Goflow, Get.
func myJob() *goflow.Job {
j := &goflow.Job{Name: "my-job", Schedule: "* * * * *"}
j.Add(&goflow.Task{
Name: "sleep-for-one-second",
Operator: goflow.Command{Cmd: "sleep", Args: []string{"1"}},
Retries: 5,
RetryDelay: goflow.ConstantDelay{Period: 1},
})
j.Add(&goflow.Task{
Name: "get-google",
Operator: goflow.Get{Client: &http.Client{}, URL: "https://www.google.com"},
})
j.Add(&goflow.Task{
Name: "add-two-plus-three",
Operator: PositiveAddition{a: 2, b: 3},
})
j.SetDownstream(j.Task("sleep-for-one-second"), j.Task("get-google"))
j.SetDownstream(j.Task("sleep-for-one-second"), j.Task("add-two-plus-three"))
return j
}By default, a task has the trigger rule allSuccessful, meaning the task starts executing when all the tasks directly
upstream exit successfully. If any dependency exits with an error, all downstream tasks are skipped, and the job exits with an error.
Sometimes you want a downstream task to execute even if there are upstream failures. Often these are situations where you want
to perform some cleanup task, such as shutting down a server. In such cases, you can give a task the trigger rule allDone.
Let's modify sleep-for-one-second to have the trigger rule allDone.
func myJob() *goflow.Job {
// other stuff
j.Add(&goflow.Task{
Name: "sleep-for-one-second",
Operator: goflow.Command{Cmd: "sleep", Args: []string{"1"}},
Retries: 5,
RetryDelay: goflow.ConstantDelay{Period: 1},
TriggerRule: "allDone",
})
// other stuff
}Finally, let's create a Goflow engine, register our job, attach a logger, and run the application.
func main() {
gf := goflow.New(goflow.Options{Streaming: true})
gf.AddJob(myJob)
gf.Use(goflow.DefaultLogger())
gf.Run(":8181")
}You can pass different options to the engine. Options currently supported:
Store: This is described in more detail below.UIPath: The path to the dashboard code. The default value is an empty string, meaning Goflow serves only the API and not the dashboard. Suggested value if you want the dashboard:ui/ShowExamples: Whether to show the example jobs. Default value:falseWithSeconds: Whether to include the seconds field in the cron spec. See the cron package documentation for details. Default value:false
Goflow is built on the Gin framework, so you can pass any Gin handler to Use.
Goflow provides several operators for common tasks. See the package documentation for details on each.
Commandexecutes a shell command.Getmakes a GET request.Postmakes a POST request.
For persisting your job execution history, Goflow allows you to plug in many different key-value stores thanks to the excellent gokv package. This way you can recover from a crash or deploy a new version of your app without losing your data.
Note: the gokv API is not yet stable. Goflow has been tested against v0.6.0.
By default, Goflow uses an in-memory database, but you can easily replace it with Postgres, Redis, S3 or any other gokv.Store. Here is an example:
package main
import "github.com/fieldryand/goflow/v2"
import "github.com/philippgille/gokv/redis"
func main() {
// create a storage client
client, err := redis.NewClient(redis.DefaultOptions)
if err != nil {
panic(err)
}
defer client.Close()
// pass the client as a Goflow option
options := goflow.Options{
Store: client,
UIPath: "ui/",
Streaming: true,
ShowExamples: true,
}
gf := goflow.New(options)
gf.Use(goflow.DefaultLogger())
gf.Run(":8181")
}You can use the API to integrate Goflow with other applications, such as an existing dashboard. Here is an overview of available endpoints:
GET /api/health: Check health of the serviceGET /api/jobs: List registered jobsGET /api/jobs/{jobname}: Get the details for a given jobGET /api/executions: Query and list job executionsPOST /api/jobs/{jobname}/submit: Submit a job for executionPOST /api/jobs/{jobname}/toggle: Toggle a job schedule on or off/stream: This endpoint returns Server-Sent Events with adatapayload matching the one returned by/api/executions. The dashboard that ships with Goflow uses this endpoint.
Check out the OpenAPI spec for more details. Easiest way is to clone the repo, then within the repo use Swagger as in the following:
docker run -p 8080:8080 -e SWAGGER_JSON=/app/swagger.json -v $(pwd):/app swaggerapi/swagger-ui![dependabot[bot] avatar](https://avatars.githubusercontent.com/in/29110?v=4 "dependabot[bot]")
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