IAM -> Policies -> Create policy

Visual editor
Service -> EC2
Actions -> Access level -> Write -> StartInstances,StopInstances
Resources -> All resources

PolicyName -> StartStopEC2Instances

IAM -> Policies -> Create policy

Visual editor
Service -> RDS
Actions -> Access level -> Write -> StartDBInstance,StopDBInstance
Resources -> All resources

PolicyName -> StartStopRDSInstances

IAM -> Roles -> Create role

AWS service -> Lambda
Policy -> StartStopEC2Instances

Role name -> StartStopEC2Instances

IAM -> Roles -> Create role

AWS service -> Lambda
Policy -> StartStopRDSInstances

Role name -> StartStopRDSInstances

AWS Lambda -> Functions -> Create function

Name -> StartEC2Instances
Runtime -> Go 1.x
Role -> Existing role -> StartStopEC2Instances

clone this repository
./build.sh

Function code
Function package -> start-ec2-instances.zip
Handler -> start-ec2-instances

Test -> Create new test event
{
  "InstanceRegion": "ap-northeast-2",
  "InstanceIdList":[
    "i-xxxxxxxxxxxxxxxxx",
    "i-xxxxxxxxxxxxxxxxx"
  ]
}

if its a RDS
{
  "InstanceRegion": "ap-northeast-2",
  "InstanceIdList":[
    "{DB_identifier_name}",
    "{DB_identifier_name2}"
  ]
}

Rules -> Create role -> Schedule

Cron expression -> xxxxx
#e.g.
00 00 ? * MON-FRI *		#9 am(GMT+9) every working day, start ec2 instances
00 10 ? * * *			#19 pm(GMT+9) every day, stop ec2 instances

Targets -> Lambda function -> StartEC2Instances
Constant(JSON text)
{
  "InstanceRegion": "ap-northeast-2",
  "InstanceIdList":[
    "i-xxxxxxxxxxxxxxxxx",
    "i-xxxxxxxxxxxxxxxxx"
  ]
}

if its a RDS
{
  "InstanceRegion": "ap-northeast-2",
  "InstanceIdList":[
    "{DB_identifier_name}",
    "{DB_identifier_name2}"
  ]
}