Faas-flow - Function Composition for OpenFaaS
- Pure FaaS with OpenFaaS
- Fast Built with
Go- Secured With
HMAC- Stateless By design
- Tracing With
open-tracing- Available As
faas-flowtemplate
Faas-flow tower visualizes and monitors flow functions
Faas-flow allows you to realize OpenFaaS function composition with ease. By defining a simple pipeline, you can orchestrate multiple functions without having to worry about the internals
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
flow.SyncNode().Apply("Func1").Apply("Func2")
return
}After building and deploying, it will give you an OpenFaaS function that orchestrates calling Func2 with the output of Func1
Faas-flow as a function composure provides the back-bone for building complex solutions and promote automation
Faas-flow can orchestrate a pipeline with long and short running function performing ETL jobs without having to orchestrate them manually or maintaining a separate application. Faas-flow ensures the execution order of several functions running in parallel or dynamically and provides rich construct to aggregate results while maintaining the intermediate data
Functions are great for isolating certain functionalities of an application. Although one still need to call the functions, write workflow logic, handle parallel processing and retries on failures. Using Faas-flow you can combine multiple OpenFaaS functions with little codes while your workflow will scale up/down automatically to handle the load
Fass-flow allows you to write function only focused on solving one problem without having to worry about the next. It makes function loosely coupled from the business logic promoting reusability. You can write the stateless function and use it across multiple applications, where Faas-flow maintains the execution state for individual workflow per requests
By supplying a number of pipeline operators, the complex composition can be achieved with little work:
The above pipelines can be achieved with little, but powerfull code:
SYNC Chain
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
flow.SyncNode().Apply("func1").Apply("func2").
Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
return
}ASYNC Chain
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
dag := flow.Dag()
dag.Node("n1").Apply("func1")
dag.Node("n2").Apply("func2").
Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
dag.Node("n3")
dag.Edge("n1", "n2")
dag.Edge("n2", "n3")
return
}PARALLEL Branching
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
dag := flow.Dag()
dag.Node("n1").Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
dag.Node("n2").Apply("func1")
dag.Node("n3").Apply("func2").Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
dag.Node("n4", faasflow.Aggregator(func(data map[string][]byte) ([]byte, error) {
// aggregate branch result data["n2"] and data["n3"]
return []byte(""), nil
}))
dag.Edge("n1", "n2")
dag.Edge("n1", "n3")
dag.Edge("n2", "n4")
dag.Edge("n3", "n4")
return
}DYNAMIC Branching
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
dag := flow.Dag()
dag.Node("n1").Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
conditionalDags := dag.ConditionalBranch("C",
[]string{"c1", "c2"}, // possible conditions
func(response []byte) []string {
// for each returned condition the corresponding branch will execute
// this function executes in the runtime of condition C
return []string{"c1", "c2"}
},
faasflow.Aggregator(func(data map[string][]byte) ([]byte, error) {
// aggregate all dynamic branches results
return []byte(""), nil
}),
)
conditionalDags["c2"].Node("n1").Apply("func1").Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
foreachDag := conditionalDags["c1"].ForEachBranch("F",
func(data []byte) map[string][]byte {
// for each returned key in the hashmap a new branch will be executed
// this function executes in the runtime of foreach F
return map[string][]byte{"f1": data, "f2": data}
},
faasflow.Aggregator(func(data map[string][]byte) ([]byte, error) {
// aggregate all dynamic branches results
return []byte(""), nil
}),
)
foreachDag.Node("n1").Modify(func(data []byte) ([]byte, error) {
// do something
return data, nil
})
dag.Node("n2")
dag.Edge("n1", "C")
dag.Edge("C", "n2")
}Full implementation of the above examples are available here
The current design consideration is made based on the below goals
- Leverage the OpenFaaS platform
- Not to violate the notions of function
- Provide flexibility, scalability, and adaptability
Faas-flow is deployed and provisioned just like any other OpenFaaS function. It allows Faas-flow to take advantage of rich functionalities available on OpenFaaS. Faas-flow provide an OpenFaaS template (faas-flow) and just like any other OpenFaaS function it can be deployed with faas-cli
Faas-flow function follows the adapter pattern. Here the adaptee is the functions and the adapter is the flow. For each node execution, Faas-flow handle the calls to the functions. Once the execution is over, it forwards an event to itself. This way the arrangement logic is separated from the functions and is implemented in the adapter. Compositions need no code instrumentations, making functions completely independent of the details of the compositions
Aggregation of separate function calls is done as chaining. Multiple functions can be called from a single node with order maintained as per the chain. This way one execution node can be implemented as an aggregator function that invokes multiple functions collects the results, optionally applies business logic, and returns a consolidated response to the client or forward to next nodes. Faas-flow fuses the adapter pattern and aggregate pattern to support more complex use cases
OpenFaaS uses Nats for event delivery and Faas-flow leverages OpenFaaS platform. Node execution in Faas-flow starts by a completion event of one or more previous nodes. A completion event denotes that all the previous dependent nodes have completed. The event carries the execution state and identifies the next node to execute. With events Faas-flow asynchronously carry-on execution of nodes by iterating itself over and over till all nodes are executed
When executing branches, one node is dependent on more than one predecessor nodes. In that scenario, the event for completion is generated by coordination of earlier nodes. Like any distributed system the coordination is achieved via a centralized service. Faas-flow keeps the logic of the coordination controller inside of Faas-flow implementation and lets the user use any external synchronous KV store by implementing StateStore
Results from function execution and intermediate data can be handled by the user manually. Faas-flow provides data-store for intermediate result storage. It automatically initializes, store, retrieve and remove data between nodes. This fits great for data processing applications. Faas-flow keeps the logic of storage controller inside of Faas-flow implementation and lets the user use any external object storage by implementing DataStore
Faas-flow design is not fixed and like any good design, it is evolving. Please contribute to make it better.
This example implements a very simple flow to Greet
Pull faas-flow template with the faas-cli
faas template pull https://github.com/s8sg/faas-flow
Create a new function using faas-flow template
faas new greet --lang faas-flowEdit function stack file greet.yml
greet:
lang: faas-flow
handler: ./greet
image: greet:latest
environment:
read_timeout: 120 # A value larger than `max` of all execution times of Nodes
write_timeout: 120 # A value larger than `max` of all execution times of Nodes
exec_timeout: 0 # disable exec timeout
write_debug: true
combine_output: false
environment_file:
- flow.ymlAdd a separate file flow.yml with faas-flow related configuration.
environment:
gateway: "gateway:8080" # The address of OpenFaaS gateway, Faas-flow use this to forward completion event
# gateway: "gateway.openfaas:8080" # For K8s
enable_tracing: false # tracing allow to trace internal node execution with opentracing
enable_hmac: true # hmac adds an extra layer of security by validating the event sourceEdit greet/handler.go and Update Define()
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
flow.SyncNode().
Modify(func(data []byte) ([]byte, error) {
result := "Hello " + string(data)
return []byte(result), nil
})
return nil
}Build and deploy
faas build
faas deployThis function will generate one Synchronous node
Modify("name") -> Hello name
All calls will be performed in one single execution of the flow function and result will be returned to the callee
Note: For flow that has more than one nodes, Faas-flow doesn't return any response. External storage or callback can be used to retrieve an async result
echo "Adam" | faas invoke greet
For each new request, faas-flow generates a unique Request Id for the flow. The same Id is used when logging
2018/08/13 07:51:59 [Request `bdojh7oi7u6bl8te4r0g`] Created
2018/08/13 07:52:03 [Request `bdojh7oi7u6bl8te4r0g`] ReceivedThe assigned request Id is set on the response header X-Faas-Flow-Reqid
One may provide custom request Id by setting X-Faas-Flow-Reqid in the request header
Request tracing can be retrieved from trace_server once enabled. Tracing is the best way to monitor flows and execution status of each node for each request
Enable tracing and add trace server as:
enable_tracing: true
trace_server: "jaegertracing:5775"jaeger (opentracing-1.x) is the tracing backend
Quick start with jaegertracing: https://www.jaegertracing.io/docs/1.8/getting-started/
Use faas-flow-tower
Retrive the requestID from X-Faas-Flow-Reqid header of response
Below is an example of tracing information for example-branching-in-Faas-flow in Faas-flow-tower
To receive a result of long running FaaSFlow request, you can specify the X-Faas-Flow-Callback-Url. FaaSFlow will invoked the callback URL with the final result and with the request ID set as X-Faas-Flow-Reqid in request Header. X-Callback-Url from OpenFaaS is not supported in FaaSFlow.
A request in faas-flow has three states :
- Running
- Paused
- Stopped
Faas-flow doesn't keep the state of a finished request
To pause a running request:
faas invoke <workflow_name> --query pause-flow=<request_id>
To resume a paused request
faas invoke <workflow_name> --query resume-flow=<request_id>
To stop an active (pasued/running) request
faas invoke <workflow_name> --query stop-flow=<request_id>
Context can be used inside definition for differet usecases. Context provide verious information such as:
HttpQuery to retrivbe original request queries
State to get flow state
Node to get current node
along with that it wraps the DataStore to store data
Context uses DataStore to store/retrive data. User can do the same by
calling Get(), Set(), and Del() from context:
flow.SyncNode().
Modify(func(data []byte) {
// parse data and set to be used later
// json.Unmarshal(&req, data)
context.Set("commitsha", req.Sha)
}).
Apply("myfunc").
Modify(func(data []byte) {
// retrieve the data that was set in the context
commitsha, _ = context.GetString("commitsha")
// use the query
})Http Query to flow can be used retrieved from context using context.Query
flow.SyncNode().Apply("myfunc", Query("auth-token", context.Query.Get("token"))). // pass as a function query
Modify(func(data []byte) {
token = context.Query.Get("token") // get query inside modifier
})Node, requestId, State is provided by the context
currentNode := context.GetNode()
requestId := context.GetRequestId()
state := context.Statefor more details check Faas-flow GoDoc
Any DAG which has a branch needs coordination for nodes completion events, also request execution state needs to me maintained. Faas-flow implements coordination controller and request state store which allows the user to use any external Synchronous KV store. User can define custom state-store with StateStore interface
type StateStore interface {
// Configure the StateStore with flow name and request ID
Configure(flowName string, requestId string)
// Initialize the StateStore (called only once in a request span)
Init() error
// Set a value (override existing, or create one)
Set(key string, value string) error
// Get a value
Get(key string) (string, error)
// Compare and Update a value
Update(key string, oldValue string, newValue string) error
// Cleanup all the resorces in StateStore (called only once in a request span)
Cleanup() error
}A StateStore can be implemented with any KV Store that provides Synchronization. The implemented StateStore can be set with DefineStateStore() at function/handler.go:
// DefineStateStore provides the override of the default StateStore
func DefineStateStore() (faasflow.StateStore, error) {
consulss, err := consulStateStore.GetConsulStateStore(os.Getenv("consul_url"), os.Getenv("consul_dc"))
return consulss, err
}StateStore is mandetory for a FaaSFlow to operate.
- ConsulStateStore statestore implementation with consul
- EtcdStateStore statewtore implementation with etcd
Faas-flow uses the DataStore to store partially completed data between nodes and request context data. Faas-flow implements a storage controller to handle storage that allows the user to use any external object-store. User can define custom data-store with DataStore interface.
type DataStore interface {
// Configure the DaraStore with flow name and request ID
Configure(flowName string, requestId string)
// Initialize the DataStore (called only once in a request span)
Init() error
// Set store a value for key, in failure returns error
Set(key string, value string) error
// Get retrives a value by key, if failure returns error
Get(key string) (string, error)
// Del delets a value by a key
Del(key string) error
// Cleanup all the resorces in DataStore
Cleanup() error
}Data Store can be implemented and set by user at the DefineDataStore() at function/handler.go:
// ProvideDataStore provides the override of the default DataStore
func DefineDataStore() (faasflow.DataStore, error) {
// initialize minio DataStore
miniods, err := minioDataStore.InitFromEnv()
return miniods, err
}DataStore is only needed for dags that stores intermediate data
- MinioDataStore allows to store data in amazon s3 or local minio DB
Finally provides an efficient way to perform post-execution steps of the flow. If specified Finally() invokes in case of both failure and success of the flow. A Finally method can be set as:
func Define(flow *faasflow.Workflow, context *faasflow.Context) (err error) {
// Define flow
flow.SyncNode().Modify(func(data []byte) {
// parse data and set to be used later
// json.Unmarshal(&req, data)
context.Set("commitsha", req.Sha)
}).
Apply("myfunc").Modify(func(data []byte) {
// retrieve the data in different node from context
commitsha, _ = context.GetString("commitsha")
})
flow.OnFailure(func(err error) {
// failure handler
})
flow.Finally(func() {
// delete the state resource
context.Del("commitsha")
})
}Issue/Suggestion Create an issue at Faas-flow-issue.
ReviewPR/Implement Create Pull Request at Faas-flow-pr.
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