Vecna is a neutered but also more versatile version of machinery, which is an asynchronous task queue/job queue based on distributed message passing.
Vecna now only supports Redis as the broker/backend, but it's designed to handle more flexible tasks, which means you can cancel the delayed tasks and periodic tasks as long as they have not been processed actually. By the way, the registered periodic tasks will not be lost even after the service is restarted.
- First Steps
- Configuration
- Custom Logger
- Server
- Workers
- Tasks
- Workflows
- Periodic Tasks & Workflows
- Cancel Delayed Tasks & Workflows
- Development
If you are familiar with Machinery, just jump to Periodic Tasks & Workflows.
Add the Vecna library to your $GOPATH/src:
go get github.com/imasker/vecnaThe config package has convenience methods for loading configuration from environment variables or a YAML file. For example, load configuration from environment variables:
cnf, err := config.NewFromEnvironment()Or load from YAML file:
cnf, err := config.NewFromYaml("config.yml", true)Second boolean flag enables live reloading of configuration every 10 seconds. Use false to disable live reloading.
Machinery configuration is encapsulated by a Config struct and injected as a dependency to objects that need it.
Use Redis URL in one of these formats:
redis://[password@]host[port][/db_num]
For example:
redis://localhost:6379, or with passwordredis://password@localhost:6379
A message broker. Currently supported brokers are:
Just me
Use Redis URL in one of these formats:
redis://[password@]host[port][/db_num]
redis+socket://[password@]/path/to/file.sock[:/db_num]
For example:
redis://localhost:6379, or with passwordredis://password@localhost:6379redis+socket://password@/path/to/file.sock:/0
Default queue name, e.g. vecna_tasks.
Result backend to use for keeping task states and results.
Currently supported backends are:
Still just me
Use Redis URL in one of these formats:
redis://[password@]host[port][/db_num]
redis+socket://[password@]/path/to/file.sock[:/db_num]
For example:
redis://localhost:6379, or with passwordredis://password@localhost:6379redis+socket://password@/path/to/file.sock:/0- cluster
redis://host1:port1,host2:port2,host3:port3 - cluster with password
redis://pass@host1:port1,host2:port2,host3:port3
How long to store task results for in seconds. Defaults to 3600 (1 hour).
Redis related configuration.
// RedisConfig ...
type RedisConfig struct {
// Maximum number of idle connections in the pool.
// Default: 10
MaxIdle int `yaml:"max_idle" envconfig:"REDIS_MAX_IDLE"`
// Maximum number of connections allocated by the pool at a given time.
// When zero, there is no limit on the number of connections in the pool.
// Default: 100
MaxActive int `yaml:"max_active" envconfig:"REDIS_MAX_ACTIVE"`
// Close connections after remaining idle for this duration in seconds. If the value
// is zero, then idle connections are not closed. Applications should set
// the timeout to a value less than the server's timeout.
// Default: 300
IdleTimeout int `yaml:"max_idle_timeout" envconfig:"REDIS_IDLE_TIMEOUT"`
// If Wait is true and the pool is at the MaxActive limit, then Get() waits
// for a connection to be returned to the pool before returning.
// Default: true
Wait bool `yaml:"wait" envconfig:"REDIS_WAIT"`
// ReadTimeout specifies the timeout in seconds for reading a single command reply.
// Default: 15
ReadTimeout int `yaml:"read_timeout" envconfig:"REDIS_READ_TIMEOUT"`
// WriteTimeout specifies the timeout in seconds for writing a single command.
// Default: 15
WriteTimeout int `yaml:"write_timeout" envconfig:"REDIS_WRITE_TIMEOUT"`
// ConnectTimeout specifies the timeout in seconds for connecting to the Redis server when
// no DialNetDial option is specified.
// Default: 15
ConnectTimeout int `yaml:"connect_timeout" envconfig:"REDIS_CONNECT_TIMEOUT"`
// NormalTasksPollPeriod specifies the period in milliseconds when polling redis for normal tasks
// Default: 1000
NormalTasksPollPeriod int `yaml:"normal_tasks_poll_period" envconfig:"REDIS_NORMAL_TASKS_POLL_PERIOD"`
// DelayedTasksPollPeriod specifies the period in milliseconds when polling redis for delayed tasks
// Default: 20
DelayedTasksPollPeriod int `yaml:"delayed_tasks_poll_period" envconfig:"REDIS_DELAYED_TASKS_POLL_PERIOD"`
DelayedTasksKey string `yaml:"delayed_tasks_key" envconfig:"REDIS_DELAYED_TASKS_KEY"`
DelayedTasksCacheKey string `yaml:"delayed_tasks_cache_key" envconfig:"REDIS_DELAYED_TASKS_CACHE_KEY"`
// PeriodicTasksKey ...
PeriodicTasksKey string `yaml:"periodic_tasks_key" envconfig:"REDIS_PERIODIC_TASKS_KEY"`
// CanceledTasksKey ...
CanceledTasksKey string `yaml:"canceled_tasks_key" envconfig:"REDIS_CANCELEDTASKSKEY"`
// MasterName specifies a redis master name in order to configure a sentinel-backed redis FailoverClient
MasterName string `yaml:"master_name" envconfig:"REDIS_MASTER_NAME"`
}You can define a custom logger by implementing the following interface:
type LoggerInterface interface {
Info(format string, a ...interface{})
Debug(format string, a ...interface{})
Warn(format string, a ...interface{})
Error(format string, a ...interface{})
Fatal(format string, a ...interface{})
Panic(format string, a ...interface{})
}Then just set the logger in your setup code by calling Set function exported by github.com/imasker/vecna/log package:
log.Set(myCustomLogger)A Machinery library must be instantiated before use. The way this is done is by creating a Server instance. Server is a base object which stores Machinery configuration and registered tasks. E.g.:
import (
"github.com/imasker/vecna"
"github.com/imasker/vecna/config"
)
cnf, err := config.NewFromYaml("config.yml", false)
// todo: handle err
server, err := vecna.NewServer(cnf)
// todo: handle errIn order to consume tasks, you need to have one or more workers running. All you need to run a worker is a Server instance with registered tasks. E.g.:
worker := server.NewWorker("worker_name", 10)
err := worker.Launch()
if err != nil {
// do something with the error
}Each worker will only consume registered tasks. For each task on the queue the Worker.Process() method will be run
in a goroutine. Use the second parameter of server.NewWorker to limit the number of concurrently running Worker.Process()
calls (per worker). Example: 1 will serialize task execution while 0 makes the number of concurrently executed tasks unlimited (default).
Tasks are a building block of Machinery applications. A task is a function which defines what happens when a worker receives a message.
Each task needs to return an error as a last return value. In addition to error tasks can now return any number of arguments.
Examples of valid tasks:
func Add(args ...int64) (int64, error) {
sum := int64(0)
for _, arg := range args {
sum += arg
}
return sum, nil
}
func Multiply(args ...int64) (int64, error) {
sum := int64(1)
for _, arg := range args {
sum *= arg
}
return sum, nil
}
// You can use context.Context as first argument to tasks, useful for open tracing
func TaskWithContext(ctx context.Context, arg Arg) error {
// ... use ctx ...
return nil
}
// Tasks need to return at least error as a minimal requirement
func DummyTask(arg string) error {
return errors.New(arg)
}
// You can also return multiple results from the task
func DummyTask2(arg1, arg2 string) (string, string, error) {
return arg1, arg2, nil
}Before your workers can consume a task, you need to register it with the server. This is done by assigning a task a unique name:
server.RegisterTasks(map[string]interface{}{
"add": Add,
"multiply": Multiply,
})Tasks can also be registered one by one:
server.RegisterTask("add", Add)
server.RegisterTask("multiply", Multiply)Simply put, when a worker receives a message like this:
{
"UUID": "48760a1a-8576-4536-973b-da09048c2ac5",
"Name": "add",
"RoutingKey": "",
"ETA": null,
"GroupUUID": "",
"GroupTaskCount": 0,
"Args": [
{
"Type": "int64",
"Value": 1,
},
{
"Type": "int64",
"Value": 1,
}
],
"Immutable": false,
"RetryCount": 0,
"RetryTimeout": 0,
"OnSuccess": null,
"OnError": null,
"ChordCallback": null,
"IgnoreWhenTaskNotRegistered": false,
"Spec": "",
"Code": ""
}It will call Add(1, 1). Each task should return an error as well so we can handle failures.
Ideally, tasks should be idempotent which means there will be no unintended consequences when a task is called multiple times with the same arguments.
A signature wraps calling arguments, execution options (such as immutability) and success/error callbacks of a task so it can be sent across the wire to workers. Task signatures implement a simple interface:
// Arg represents a single argument passed to invocation fo a task
type Arg struct {
Type string
Value interface{}
}
// Headers represents the headers which should be used to direct the task
type Headers map[string]interface{}
// Signature represents a single task invocation
type Signature struct {
UUID string
Name string
RoutingKey string
ETA *time.Time
GroupUUID string
GroupTaskCount int
Args []Arg
Headers Headers
Immutable bool
RetryCount int
RetryTimeout int
OnSuccess []*Signature
OnError []*Signature
ChordCallback *Signature
IgnoreWhenTaskNotRegistered bool
Spec string
Code string
}UUID is a unique ID of a task. You can either set it yourself or it will be automatically generated.
Name is the unique task name by which it is registered against a Server instance.
RoutingKey is used for routing a task to correct queue. If you leave it empty, the default behaviour will be to set it to the default queue's binding key for direct exchange type and to the default queue name for other exchange types.
ETA is a timestamp used for delaying a task. if it's nil, the task will be published for workers to consume immediately. If it is set, the task will be delayed until the ETA timestamp.
GroupUUID, GroupTaskCount are useful for creating groups of tasks.
Args is a list of arguments that will be passed to the task when it is executed by a worker.
Headers is a list of headers that will be used when publishing the task to AMQP queue.
Immutable is a flag which defines whether a result of the executed task can be modified or not. This is important with OnSuccess callbacks. Immutable task will not pass its result to its success callbacks while a mutable task will prepend its result to args sent to callback tasks. Long story short, set Immutable to false if you want to pass result of the first task in a chain to the second task.
RetryCount specifies how many times a failed task should be retried (defaults to 0). Retry attempts will be spaced out in time, after each failure another attempt will be scheduled further to the future.
RetryTimeout specifies how long to wait before resending task to the queue for retry attempt. Default behaviour is to use fibonacci sequence to increase the timeout after each failed retry attempt.
OnSuccess defines tasks which will be called after the task has executed successfully. It is a slice of task signature structs.
OnError defines tasks which will be called after the task execution fails. The first argument passed to error callbacks will be the error string returned from the failed task.
ChordCallback is used to create a callback to a group of tasks.
IgnoreWhenTaskNotRegistered auto removes the request when there is no handler available. When this is true a task with no handler will be ignored and not placed back in the queue
Spec marks this task being a periodic task. It requires 5 entries representing: minute, hour, day of month, month and day of week, in that order.
Code Every task in group or in periodic tasks has the same code, so that we can cancel the task by using this code. By default, code will be the GroupID if exists or ID. It can also be specified by the user.
Machinery encodes tasks to JSON before sending them to the broker. Task results are also stored in the backend as JSON encoded strings. Therefor only types with native JSON representation can be supported. Currently supported types are:
boolintint8int16int32int64uintuint8uint16uint32uint64float32float64string[]bool[]int[]int8[]int16[]int32[]int64[]uint[]uint8[]uint16[]uint32[]uint64[]float32[]float64[]string
Tasks can be called by passing an instance of Signature to an Server instance. E.g:
import (
"github.com/imasker/vecna/tasks"
)
signature := &tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
asyncResult, err := server.SendTask(signature)
if err != nil {
// failed to send the task
// do something with the error
}You can delay a task by setting the ETA timestamp field on the task signature.
// Delay the task by 5 seconds
eta := time.Now().UTC().Add(time.Second * 5)
signature.ETA = &etaYou can set a number of retry attempts before declaring task as failed. Fibonacci sequence will be used to space out retry requests over time. (See RetryTimeout for details.)
// If the task fails, retry it up to 3 times
signature.RetryCount = 3Alternatively, you can return tasks.ErrRetryTaskLater from your task and specify duration after which the task should be retried, e.g.:
return tasks.NewErrRetryTaskLater("some error", 4 * time.Hour)Tasks currently waiting in the queue to be consumed by workers can be inspected, e.g.:
server.GetBroker().GetPendingTasks("some_queue")Currently only supported by Redis broker.
If you configure a result backend, the task states and results will be persisted. Possible states:
const (
// StatePending - initial state of a task
StatePending = "PENDING"
// StateReceived - when task is received by a worker
StateReceived = "RECEIVED"
// StateStarted - when the worker starts processing the task
StateStarted = "STARTED"
// StateRetry - when failed task has been scheduled for retry
StateRetry = "RETRY"
// StateSuccess - when the task is processed successfully
StateSuccess = "SUCCESS"
// StateFailure - when processing of the task fails
StateFailure = "FAILURE"
// StateCanceled - when the task is canceled
StateCanceled = "CANCELED"
)// TaskResult represents an actual return value of a processed task
type TaskResult struct {
Type string
Value interface{}
}
// TaskState represents a state of a task
type TaskState struct {
TaskID string
State string
Results []*TaskResult
Error string
}
// GroupMeta stores useful metadata about tasks within the same group
// E.g. UUIDs of all tasks which are used in order to check if all tasks
// completed successfully or not and thus whether to trigger chord callback
type GroupMeta struct {
GroupID string
TaskIDs []string
ChordTriggered bool
Lock bool
}TaskResult represents a slice of return values of a processed task.
TaskState struct will be serialized and stored every time a task state changes.
GroupMeta stores useful metadata about tasks within the same group. E.g. UUIDs of all tasks which are used in order to check if all tasks completed successfully or not and thus whether to trigger chord callback.
AsyncResult object allows you to check for the state of a task:
taskState := asyncResult.GetState()
fmt.Printf("Current state of %v task is:\n", taskState.TaskUUID)
fmt.Println(taskState.State)There are couple of convenient methods to inspect the task status:
asyncResult.GetState().IsCompleted()
asyncResult.GetState().IsSuccess()
asyncResult.GetState().IsFailure()
asyncResult.GetState().IsCanceled()You can also do a synchronous blocking call to wait for a task result:
results, err := asyncResult.Get(time.Duration(time.Millisecond * 5))
if err != nil {
// getting result of a task failed
// do something with the error
}
for _, result := range results {
fmt.Println(result.Interface())
}When a task returns with an error, the default behavior is to first attempty to retry the task if it's retriable, otherwise log the error and then eventually call any error callbacks.
To customize this, you can set a custom error handler on the worker which can do more than just logging after retries fail and error callbacks are trigerred:
worker.SetErrorHandler(func (signature *tasks.Signature, err error) {
customHandler(signature, err)
})Running a single asynchronous task is fine but often you will want to design a workflow of tasks to be executed in an orchestrated way. There are couple of useful functions to help you design workflows.
Group is a set of tasks which will be executed in parallel, independent of each other. E.g.:
import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
group, _ := tasks.NewGroup(&signature1, &signature2)
asyncResults, err := server.SendGroup(group, 0) //The second parameter specifies the number of concurrent sending tasks. 0 means unlimited.
if err != nil {
// failed to send the group
// do something with the error
}SendGroup returns a slice of AsyncResult objects. So you can do a blocking call and wait for the result of groups tasks:
for _, asyncResult := range asyncResults {
results, err := asyncResult.Get(time.Duration(time.Millisecond * 5))
if err != nil {
// getting result of a task failed
// do something with the error
}
for _, result := range results {
fmt.Println(result.Interface())
}
}Chord allows you to define a callback to be executed after all tasks in a group finished processing, e.g.:
import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
signature3 := tasks.Signature{
Name: "multiply",
}
group := tasks.NewGroup(&signature1, &signature2)
chord, _ := tasks.NewChord(group, &signature3)
chordAsyncResult, err := server.SendChord(chord, 0) //The second parameter specifies the number of concurrent sending tasks. 0 means unlimited.
if err != nil {
// failed to send the chord
// do something with the error
}The above example executes task1 and task2 in parallel, aggregates their results and passes them to task3. Therefore what would end up happening is:
multiply(add(1, 1), add(5, 5))
More explicitly:
(1 + 1) * (5 + 5) = 2 * 10 = 20
SendChord returns ChordAsyncResult which follows AsyncResult's interface. So you can do a blocking call and wait for the result of the callback:
results, err := chordAsyncResult.Get(time.Duration(time.Millisecond * 5))
if err != nil {
// getting result of a chord failed
// do something with the error
}
for _, result := range results {
fmt.Println(result.Interface())
}Chain is simply a set of tasks which will be executed one by one, each successful task triggering the next task in the chain. E.g.:
import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
signature3 := tasks.Signature{
Name: "multiply",
Args: []tasks.Arg{
{
Type: "int64",
Value: 4,
},
},
}
chain, _ := tasks.NewChain(&signature1, &signature2, &signature3)
chainAsyncResult, err := server.SendChain(chain)
if err != nil {
// failed to send the chain
// do something with the error
}The above example executes task1, then task2 and then task3. When a task is completed successfully, the result is appended to the end of list of arguments for the next task in the chain. Therefore what would end up happening is:
multiply(4, add(5, 5, add(1, 1)))
More explicitly:
4 * (5 + 5 + (1 + 1)) # task1: add(1, 1) returns 2
= 4 * (5 + 5 + 2) # task2: add(5, 5, 2) returns 12
= 4 * (12) # task3: multiply(4, 12) returns 48
= 48
SendChain returns ChainAsyncResult which follows AsyncResult's interface. So you can do a blocking call and wait for the result of the whole chain:
results, err := chainAsyncResult.Get(time.Duration(time.Millisecond * 5))
if err != nil {
// getting result of a chain failed
// do something with the error
}
for _, result := range results {
fmt.Println(result.Interface())
}This part is why Vecna exists. You can schedule periodic tasks and cancel them freely. Just remember to save the task code.
import (
"github.com/imasker/vecna/tasks"
)
signature := &tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
_, err := server.SendPeriodicTask("0 6 * * ?", signature)
if err != nil {
// failed to send periodic task
}
// remember to save the task code `signature.Code`, you can use it to cancel this periodic taskimport (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
group, _ := tasks.NewGroup(&signature1, &signature2)
_, err := server.SendPeriodicGroup("0 6 * * ?", group)
if err != nil {
// failed to send periodic group
}
// remember to save the task code `group.Tasks[0].Code`, you can use it to cancel this periodic groupimport (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
signature3 := tasks.Signature{
Name: "multiply",
Args: []tasks.Arg{
{
Type: "int64",
Value: 4,
},
},
}
chain, _ := tasks.NewChain(&signature1, &signature2, &signature3)
err := server.RegisterPeriodicChain("0 6 * * ?", "periodic-chain", chain)
if err != nil {
// failed to register periodic chain
}
// remember to save the task code `chain.Tasks[0].Code`, you can use it to cancel this periodic chainimport (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
signature1 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 1,
},
{
Type: "int64",
Value: 1,
},
},
}
signature2 := tasks.Signature{
Name: "add",
Args: []tasks.Arg{
{
Type: "int64",
Value: 5,
},
{
Type: "int64",
Value: 5,
},
},
}
signature3 := tasks.Signature{
Name: "multiply",
}
group := tasks.NewGroup(&signature1, &signature2)
chord, _ := tasks.NewChord(group, &signature3)
err := server.SendPeriodicChord("0 6 * * ?", chord)
if err != nil {
// failed to send periodic chord
}
// remember to save the task code `chord.Group.Tasks[0].Code`, you can use it to cancel this periodic chordimport (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
// use the code you have saved and the taskType if you used a user-defined taskID
err := server.CancelPeriodicTask(code, "")
if err != nil {
// failed to cancel periodic task
}To cancel the delayed tasks, you have to save the Signature/Chain/Group/Chord or at least their IDs of every Signature to reconstruct the struct.
import (
"github.com/imasker/vecna/tasks"
)
var signature *tasks.Signature
// todo: try to find your signature before canceling it
_, err := server.CancelDelayedTask(signature)
if err != nil {
// failed to cancel delayed task
}import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
var group *tasks.Group
// todo: try to find your group before canceling it
_, err := server.CancelDelayedGroup(group)
if err != nil {
// failed to cancel delayed group
}import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
var chain *tasks.Chain
// todo: try to find your chain before canceling it
_, err := server.CancelDelayedChain(chain)
if err != nil {
// failed to cancel delayed chain
}import (
"github.com/imasker/vecna/tasks"
"github.com/imasker/vecna"
)
var chord *tasks.Chord
// todo: try to find your chord before canceling it
_, err := server.CancelDelayedChord(chord)
if err != nil {
// failed to cancel delayed chord
}- Go
- Redis (Optional)
On OS X systems, you can install requirements using Homebrew:
brew install goSince Go 1.11, a new recommended dependency management system is via modules.
go test $(go list ./...)