Hope someone can help enlighten me on this issue. I am currently working on a lambda function that utilizes the cloud watch scheduler to check various devices and it is using elasticache to maintain a simple database on the readings.
My problem is that after I shut down my testing at night. I fire up the lambda function in the morning and the function has lost access to the internet. Which is represented by the function timing out. Regularly after a few hour of messing around with my routes and my vpc settings it will start working again. Just to break the following day. Sometimes it works with nat gateway other times with just a nat instance. The changes I typically make to the vpc set up are minor. The pattern for the set up I use is one public and one private and one natgateway.
Update: After not being able to access the internet from my VPC all day yesterday, today is functioning fine. What did I do differently, nothing. When it stops functioning again, probably later today, I will be calling up AWS to see if we can get to the bottom of this.
A Lambda function with VPC access will require a NAT gateway to access the internet. You state that it sometimes works with only an Internet Gateway, but that isn't possible according to the AWS documentation. If you are removing the NAT gateway, or the VPC's route to the NAT gateway, then that would remove internet access from any Lambda functions that have VPC access enabled.
来源：https://stackoverflow.com/questions/36581147/aws-vpc-lambda-function-keeps-losing-internet-access