amazon web services - connecting AWS SAM Local with dynamodb in docker

Question

I've set up an api gateway/aws lambda pair using AWS sam local and confirmed I can call it successfully after running

sam local start-api

I've then added a local dynamodb instance in a docker container and created a table on it using the aws cli

But, having added the code to the lambda to write to the dynamodb instance I receive:

2018-02-22T11:13:16.172Z ed9ab38e-fb54-18a4-0852-db7e5b56c8cd error: could not write to table: {"message":"connect ECONNREFUSED 0.0.0.0:8000","code":"NetworkingError","errno":"ECONNREFUSED","syscall":"connect","address":"0.0.0.0","port":8000,"region":"eu-west-2","hostname":"0.0.0.0","retryable":true,"time":"2018-02-22T11:13:16.165Z"} writing event from command: {"name":"test","geolocation":"xyz","type":"createDestination"} END RequestId: ed9ab38e-fb54-18a4-0852-db7e5b56c8cd

I saw online that you might need to connect to the same docker network so I created a network docker network create lambda-local and have changed my start commands to:

sam local start-api --docker-network lambda-local

and

docker run -v "$PWD":/dynamodb_local_db -p 8000:8000 --network=lambda-local cnadiminti/dynamodb-local:latest

but still receive the same error

sam local is printing out 2018/02/22 11:12:51 Connecting container 98b19370ab92f3378ce380e9c840177905a49fc986597fef9ef589e624b4eac3 to network lambda-local

I'm creating the dynamodbclient using:

const AWS = require('aws-sdk')
const dynamodbURL = process.env.dynamodbURL || 'http://0.0.0.0:8000'
const awsAccessKeyId = process.env.AWS_ACCESS_KEY_ID || '1234567'
const awsAccessKey = process.env.AWS_SECRET_ACCESS_KEY || '7654321'
const awsRegion = process.env.AWS_REGION || 'eu-west-2'

console.log(awsRegion, 'initialising dynamodb in region: ')

let dynamoDbClient
const makeClient = () => {
  dynamoDbClient = new AWS.DynamoDB.DocumentClient({
    endpoint: dynamodbURL,
    accessKeyId: awsAccessKeyId,
    secretAccessKey: awsAccessKey,
    region: awsRegion
  })
  return dynamoDbClient
}

module.exports = {
  connect: () => dynamoDbClient || makeClient()
}

and inspecting the dynamodbclient my code is creating shows

DocumentClient {
  options:
   { endpoint: 'http://0.0.0.0:8000',
     accessKeyId: 'my-key',
     secretAccessKey: 'my-secret',
     region: 'eu-west-2',
     attrValue: 'S8' },
  service:
   Service {
     config:
      Config {
        credentials: [Object],
        credentialProvider: [Object],
        region: 'eu-west-2',
        logger: null,
        apiVersions: {},
        apiVersion: null,
        endpoint: 'http://0.0.0.0:8000',
        httpOptions: [Object],
        maxRetries: undefined,
        maxRedirects: 10,
        paramValidation: true,
        sslEnabled: true,
        s3ForcePathStyle: false,
        s3BucketEndpoint: false,
        s3DisableBodySigning: true,
        computeChecksums: true,
        convertResponseTypes: true,
        correctClockSkew: false,
        customUserAgent: null,
        dynamoDbCrc32: true,
        systemClockOffset: 0,
        signatureVersion: null,
        signatureCache: true,
        retryDelayOptions: {},
        useAccelerateEndpoint: false,
        accessKeyId: 'my-key',
        secretAccessKey: 'my-secret' },
     endpoint:
      Endpoint {
        protocol: 'http:',
        host: '0.0.0.0:8000',
        port: 8000,
        hostname: '0.0.0.0',
        pathname: '/',
        path: '/',
        href: 'http://0.0.0.0:8000/' },
     _clientId: 1 },
  attrValue: 'S8' }

Should this setup work? How do I get them talking to each other?

---- edit ----

Based on a twitter conversation it's worth mentioning (maybe) that I can interact with dynamodb at the CLI and in the web shell

Answer 1

Many thanks to Heitor Lessa who answered me on Twitter with an example repo

Which pointed me at the answer...

• dynamodb's docker container is on 127.0.0.1 from the context of my machine (which is why I could interact with it)

• SAM local's docker container is on 127.0.0.1 from the context of my machine

• But they aren't on 127.0.0.1 from each other's context

So: https://github.com/heitorlessa/sam-local-python-hot-reloading/blob/master/users/users.py#L14

Pointed me at changing my connection code to:

const AWS = require('aws-sdk')
const awsRegion = process.env.AWS_REGION || 'eu-west-2'

let dynamoDbClient
const makeClient = () => {
  const options = {
    region: awsRegion
  }
  if(process.env.AWS_SAM_LOCAL) {
    options.endpoint = 'http://dynamodb:8000'
  }
  dynamoDbClient = new AWS.DynamoDB.DocumentClient(options)
  return dynamoDbClient
}

module.exports = {
  connect: () => dynamoDbClient || makeClient()
}

with the important lines being:

if(process.env.AWS_SAM_LOCAL) {
  options.endpoint = 'http://dynamodb:8000'
}

from the context of the SAM local docker container the dynamodb container is exposed via its name

My two startup commands ended up as:

docker run -d -v "$PWD":/dynamodb_local_db -p 8000:8000 --network lambda-local --name dynamodb cnadiminti/dynamodb-local

and

AWS_REGION=eu-west-2 sam local start-api --docker-network lambda-local

with the only change here being to give the dynamodb container a name