DockerforDynamoDb.md

Docker for DynamoDb

This document describes how to use docker-compose to start a container with DynamoDb locally, add a table and connect to it from .NET Core.

Table attributes

You can create the table by getting the table attributes using the describe-table operation

aws dynamodb describe-table --table-name some.table > table.json

docker-compose.yml

Below is the service description for using DynamoDb with added comments. This refers to version 3.7 of the compose file.

  dynamodb:
    build:
      context: ../Infrastructure/Docker/DynamoDB/ # Location of the Dockerfile
    environment:
      - HOSTNAME_EXTERNAL=dynamodb                # Name of the host to expose the services externally 
      - SERVICES=dynamodb                         # List of AWS services to start, seperated by a comma ","
      - AWS_DEFAULT_REGION=ap-southeast-2         # AWS region
      - AWS_ACCESS_KEY_ID=foo                     # AWS Access Key - I use "foo" for all services
      - AWS_SECRET_ACCESS_KEY=bar                 # AWS Secret Key - I use "bar" for all services
    ports:
      - "4569:4569"                               # Number of port to expose externally

Dockerfile

Below are the commands used to create the container with added comments.

# Image to use. I found version 0.9.6 to be very stable
FROM localstack/localstack:0.9.6
# Number of port to expose externally
EXPOSE 4569

# Copy in table creation scripts. The directory below should be in the same directory as the Dockerfile
COPY ./docker-entrypoint-initaws.d /docker-entrypoint-initaws.d

docker-entrypoint-initaws.d

Localstack will attempt to run all files in the docker-entrypoint-initaws.d directory*
Create a shell file with the following contents:

aws --endpoint-url http://dynamodb:4569 --region ap-southeast-2 \
    dynamodb create-table --cli-input-json file:///docker-entrypoint-initaws.d/table.json

* Make sure your files are saved with line feeds. Add the following to your .gitattributes

*.sh text eol=lf

Image choice

There are currently 2 options to create a local instance of DynamoDb

1. localstack
   https://github.com/localstack/localstack
2. DynamoDB Local
   https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DynamoDBLocal.html

I choose to go with localstack as it uses the same creation mechanism for every AWS component i.e. you just copy scripts into the docker-entrypoint-initaws.d directory and localstack will process them.

Running docker-compose

You can now start DynamoDb using:

docker-compose --file docker-compose.yml up --build

.NET Core and AmazonDynamoDBClient

By default all amazon clients try to connect to AWS in the cloud. You will need to pass in a service URL to configure the client to use the container.

services.AddSingleton<IAmazonDynamoDB>(client =>
{
    if (string.IsNullOrEmpty(awsConfig.DynamoDbServiceUrl))
    {
        return new AmazonDynamoDBClient(credentials, region);
    }

    // Localstack support
    var config = new AmazonDynamoDBConfig
    {
        ServiceURL = awsConfig.DynamoDbServiceUrl
    };
    // Dynamo won't work with empty credentials
    return new AmazonDynamoDBClient(new BasicAWSCredentials("foo", "bar"), config);
});