In this article we’ll take a look on how to use AWS Step Functions to manage long running jobs. This is very common task for any process orchestration system and it is build on top of Iterating a Loop Using Lambda example from official AWS documentation.
As an example of long running process, we’ll take RDS instance snapshot creation process.
Our AWS Step Functions state machine will consist of:
- Task, which initiate create RDS Snapshot process (implemented using Lambda Function)
- Wait 1 minute state
- Task, which describes RDS Snapshot Lambda Function
- Choise state, which checks DB Snapshot status and either waits, either continue flow control to two stubs
- Pass state, which represents state machine success or failed execution status; in our case both states does nothing, but you may use them to do extra work, like sending SNS notifications or calling other AWS services
Create RDS Snapshot Lambda Function
import boto3
import datetime
import math
RDS_CLIENT = boto3.client('rds')
def handler(event,context):
print('Event: {}'.format(event))
now = datetime.datetime.now()
timestamp = math.ceil(datetime.datetime.timestamp(now))
params = {
'DBSnapshotIdentifier': '${db_instance_identifier}-rds-snapshot-{}'.format(
timestamp
),
'DBInstanceIdentifier': '${db_instance_identifier}'
}
response = RDS_CLIENT.create_db_snapshot(**params)
return {
'DBSnapshot': {
'DBSnapshotIdentifier': response['DBSnapshot']['DBSnapshotIdentifier'],
'DBInstanceIdentifier': response['DBSnapshot']['DBInstanceIdentifier']
}
}
Our function takes DBSnapshotIdentifier and DBInstanceIdentifier as parameters and calling create_db_snapshot() function. As a result of operation we’re sending Python dict to the next state in state machine (Describe RDS Snapshot Lambda Function)
Describe RDS Snapshot Lambda Function
import boto3
import datetime
RDS_CLIENT = boto3.client('rds')
def handler(event,context):
print('Event: {}'.format(event))
db_snapshot_identifier = event['DBSnapshot']['DBSnapshotIdentifier']
db_instance_identifier = event['DBSnapshot']['DBInstanceIdentifier']
response = RDS_CLIENT.describe_db_snapshots(
DBSnapshotIdentifier=db_snapshot_identifier,
DBInstanceIdentifier=db_instance_identifier,
SnapshotType='manual'
)
return {
'DBSnapshot': {
'DBSnapshotIdentifier': response['DBSnapshots'][0]['DBSnapshotIdentifier'],
'DBInstanceIdentifier': response['DBSnapshots'][0]['DBInstanceIdentifier'],
'Status': response['DBSnapshots'][0]['Status']
}
}
This function is even simplier, because it just takes passed parameters from the previous step, does describe_db_snapshots() and returning the same dict with snapshot operation status.
State machine
AWS Step Functions state machine description. Our graph consists of the following steps
- Create snapshot
- Wait 1 minute
- Get snapshot status
- Snapshot completed?
- Done
- Failed
{
"Comment": "State machine to create RDS DB instance Snapshot",
"StartAt": "Create snapshot",
"States": {
"Create snapshot": {
"Type": "Task",
"Resource": "${create_snapshot_lambda_arn}",
"Next": "Wait 1 minute"
},
"Wait 1 minute": {
"Type": "Wait",
"Seconds": 60,
"Next": "Get snapshot status"
},
"Get snapshot status": {
"Type": "Task",
"Resource": "${get_snapshot_status_lambda_arn}",
"Next": "Snapshot completed?"
},
"Snapshot completed?": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.DBSnapshot.Status",
"StringEquals": "available",
"Next": "Done"
},
{
"Variable": "$.DBSnapshot.Status",
"StringEquals": "failed",
"Next": "Failed"
}
],
"Default": "Wait 1 minute"
},
"Done": {
"Type": "Pass",
"End": true
},
"Failed": {
"Type": "Pass",
"End": true
}
}
}
Complete example
And finally, here’s the complete CloudFormation stack template, tying everything alltogether:
AWSTemplateFormatVersion: 2010-09-09
Description: >
This stack is creating RDS instance snapshot and wait till process finishes.
Parameters:
DBInstanceIdentifier:
Description: >
Identifier of RDS DB instance
Type: String
Resources:
LambdaIamRole:
Type: 'AWS::IAM::Role'
Properties:
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
-
Effect: Allow
Principal:
Service:
- lambda.amazonaws.com
Action:
- 'sts:AssumeRole'
Path: /
Policies:
-
PolicyName: root
PolicyDocument:
Version: 2012-10-17
Statement:
-
Effect: Allow
Action:
- 'rds:CreateDBSnapshot'
- 'rds:DescribeDBSnapshots'
Resource: '*'
-
Effect: Allow
Action:
- 'logs:CreateLogGroup'
- 'logs:CreateLogStream'
- 'logs:PutLogEvents'
Resource: 'arn:aws:logs:*:*:*'
CreateSnapshotLambda:
Type: AWS::Lambda::Function
Properties:
Handler: index.handler
Role: !GetAtt LambdaIamRole.Arn
Runtime: python3.6
Timeout: 30
Code:
ZipFile:
!Sub
- |-
import boto3
import datetime
import math
RDS_CLIENT = boto3.client('rds')
def handler(event,context):
print('Event: {}'.format(event))
now = datetime.datetime.now()
timestamp = math.ceil(datetime.datetime.timestamp(now))
params = {
'DBSnapshotIdentifier': '${db_instance_identifier}-rds-snapshot-{}'.format(
timestamp
),
'DBInstanceIdentifier': '${db_instance_identifier}'
}
response = RDS_CLIENT.create_db_snapshot(**params)
return {
'DBSnapshot': {
'DBSnapshotIdentifier': response['DBSnapshot']['DBSnapshotIdentifier'],
'DBInstanceIdentifier': response['DBSnapshot']['DBInstanceIdentifier']
}
}
-
db_instance_identifier:
!Sub '${DBInstanceIdentifier}'
DescribeSnapshotLambda:
Type: AWS::Lambda::Function
Properties:
Handler: index.handler
Role: !GetAtt LambdaIamRole.Arn
Runtime: python3.6
Timeout: 30
Code:
ZipFile: |
import boto3
import datetime
RDS_CLIENT = boto3.client('rds')
def handler(event,context):
print('Event: {}'.format(event))
db_snapshot_identifier = event['DBSnapshot']['DBSnapshotIdentifier']
db_instance_identifier = event['DBSnapshot']['DBInstanceIdentifier']
response = RDS_CLIENT.describe_db_snapshots(
DBSnapshotIdentifier=db_snapshot_identifier,
DBInstanceIdentifier=db_instance_identifier,
SnapshotType='manual'
)
return {
'DBSnapshot': {
'DBSnapshotIdentifier': response['DBSnapshots'][0]['DBSnapshotIdentifier'],
'DBInstanceIdentifier': response['DBSnapshots'][0]['DBInstanceIdentifier'],
'Status': response['DBSnapshots'][0]['Status']
}
}
StateMachineExecutionRole:
Type: "AWS::IAM::Role"
Properties:
AssumeRolePolicyDocument:
Version: "2012-10-17"
Statement:
-
Effect: "Allow"
Principal:
Service:
- !Sub states.${AWS::Region}.amazonaws.com
Action: "sts:AssumeRole"
Path: "/"
Policies:
-
PolicyName: StatesExecutionPolicy
PolicyDocument:
Version: "2012-10-17"
Statement:
-
Effect: Allow
Action:
- "lambda:InvokeFunction"
Resource: "*"
StateMachine:
Type: "AWS::StepFunctions::StateMachine"
Properties:
DefinitionString:
!Sub
- |-
{
"Comment": "State machine to create RDS DB instance Snapshot",
"StartAt": "Create snapshot",
"States": {
"Create snapshot": {
"Type": "Task",
"Resource": "${create_snapshot_lambda_arn}",
"Next": "Wait 1 minute"
},
"Wait 1 minute": {
"Type": "Wait",
"Seconds": 60,
"Next": "Get snapshot status"
},
"Get snapshot status": {
"Type": "Task",
"Resource": "${get_snapshot_status_lambda_arn}",
"Next": "Snapshot completed?"
},
"Snapshot completed?": {
"Type": "Choice",
"Choices": [
{
"Variable": "$.DBSnapshot.Status",
"StringEquals": "available",
"Next": "Done"
},
{
"Variable": "$.DBSnapshot.Status",
"StringEquals": "failed",
"Next": "Failed"
}
],
"Default": "Wait 1 minute"
},
"Done": {
"Type": "Pass",
"End": true
},
"Failed": {
"Type": "Pass",
"End": true
}
}
}
-
create_snapshot_lambda_arn: !GetAtt [ CreateSnapshotLambda, Arn ]
get_snapshot_status_lambda_arn: !GetAtt [ DescribeSnapshotLambda, Arn ]
RoleArn: !GetAtt [ StateMachineExecutionRole, Arn ]
Outputs:
StateMachine:
Value: !Ref StateMachine
Description: Step Function workflow Arn
Hope, that will save you some amount of time.
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