Putting to local DynamoDB table with Python boto3 times out - aws-lambda

Question

I am attempting to programmatically put data into a locally running DynamoDB Container by triggering a Python lambda expression.
I'm trying to follow the template provided here: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/GettingStarted.Python.03.html
I am using the amazon/dynamodb-local you can download here: https://hub.docker.com/r/amazon/dynamodb-local
Using Ubuntu 18.04.2 LTS to run the container and lambda server
AWS Sam CLI to run my Lambda api
Docker Version 18.09.4
Python 3.6 (You can see this in sam logs below)
Startup command for python lambda is just "sam local start-api"
First my Lambda Code
import json
import boto3
def lambda_handler(event, context):
print("before grabbing dynamodb")
# dynamodb = boto3.resource('dynamodb', endpoint_url="http://localhost:8000",region_name='us-west-2',AWS_ACCESS_KEY_ID='RANDOM',AWS_SECRET_ACCESS_KEY='RANDOM')
dynamodb = boto3.resource('dynamodb', endpoint_url="http://localhost:8000")
table = dynamodb.Table('ContactRequests')
try:
response = table.put_item(
Item={
'id': "1234",
'name': "test user",
'email': "testEmail#gmail.com"
}
)
print("response: " + str(response))
return {
"statusCode": 200,
"body": json.dumps({
"message": "hello world"
}),
}
I know that I should have this table ContactRequests available at localhost:8000, because I can run this script to view my docker container dynamodb tables
I have tested this with a variety of values in the boto.resource call to include the access keys, region names, and secret keys, with no improvement to result
dev#ubuntu:~/Projects$ aws dynamodb list-tables --endpoint-url http://localhost:8000
{
"TableNames": [
"ContactRequests"
]
}
I am also able to successfully hit the localhost:8000/shell that dynamodb offers
Unfortunately while running, if I hit the endpoint that triggers this method, I get a timeout that logs like so
Fetching lambci/lambda:python3.6 Docker container image......
2019-04-09 15:52:08 Mounting /home/dev/Projects/sam-app/.aws-sam/build/HelloWorldFunction as /var/task:ro inside runtime container
2019-04-09 15:52:12 Function 'HelloWorldFunction' timed out after 3 seconds
2019-04-09 15:52:13 Function returned an invalid response (must include one of: body, headers or statusCode in the response object). Response received:
2019-04-09 15:52:13 127.0.0.1 - - [09/Apr/2019 15:52:13] "GET /hello HTTP/1.1" 502 -
Notice that none of my print methods are being triggered, if I remove the call to table.put, then the print methods are successfully called.
I've seen similar questions on Stack Overflow such as this lambda python dynamodb write gets timeout error that state that the problem is I am using a local db, but shouldn't I still be able to write to a local db with boto3, if I point it to my locally running dynamodb instance?

Answer 1

Your Docker container running the Lambda function can't reach the DynamoDB at 127.0.0.1. Try instead the name of your DynamoDB local docker container as the host name for the endpoint:
dynamodb = boto3.resource('dynamodb', endpoint_url="http://<DynamoDB_LOCAL_NAME>:8000")
You can use docker ps to find the <DynamoDB_LOCAL_NAME> or give it a name:
docker run --name dynamodb amazon/dynamodb-local
and then connect:
dynamodb = boto3.resource('dynamodb', endpoint_url="http://dynamodb:8000")

Answer 2

Found the solution to the problem here: connecting AWS SAM Local with dynamodb in docker
The question asker noted that he saw online that he may need to connect to the same docker network using:
docker network create lambda-local
So created this network, then updated my sam command and my docker commands to use this network, like so:
docker run --name dynamodb -p 8000:8000 --network=local-lambda amazon/dynamodb-local
sam local start-api --docker-network local-lambda
After that I no longer experienced the timeout issue.
I'm still working on understanding exactly why this was the issue
To be fair though, it was important that I use the dynamodb container name as the host for my boto3 resource call as well.
So in the end, it was a combination of the solution above and the answer provided by "Reto Aebersold" that created the final solution
dynamodb = boto3.resource('dynamodb', endpoint_url="http://<DynamoDB_LOCAL_NAME>:8000")