A Real World PHP Lambda App Part 4: Setting up DynamoDb Locally

Submitted by nigel on Sunday 4th February 2018
We will be using DynamoDb to save our vote data, but since this adds additional complexity to the development process, it will also slow it down. There is a solution - DynamoDb can be installed locally so that there isn't the need for continuous deploys to AWS. In fact, the local version of DynamoDb is probably SQLite but it will do the job whilst we are testing our code. It also requires a working Java runtime so that needs to be installed first. This can be done on the command line. I am using Ubuntu 16.04 so for my system I do:
$ sudo apt-get update
$ sudo apt-get install default-jre
The JAVA_HOME environment variable will need to be set for the local DynamoDb to work correctly. Firstly we must determine where Java has been installed.
$ sudo update-alternatives --config java
There is only one alternative in link group java (providing /usr/bin/java): /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java
Nothing to configure.
That's easy - Java is available at /usr/bin/java. Now edit /etc/environment and add the following line at the bottom:
JAVA_HOME="/usr/bin/java"
Now we need to reload and check the variable is set
$ source /etc/environment 
$ echo $JAVA_HOME
/usr/bin/java
Install DynamoDb
I downloaded the DynamoDb tarball from the AWS site and moved it into my /tmp directory.
$ cd /usr/lib
$ sudo mkdir /dynamodb
$ cd dynamodb
$ tar zxvf /tmp/dynamodb_local_latest.tar.gz 
Now list the directory and you'll see the jar file we will need to run.
$ ls -las
total 3660
   4 drwxr-xr-x  4 root root    4096 Feb  4 17:55 .
   4 drwxr-xr-x 69 root root    4096 Feb  4 17:54 ..
3628 -rw-r--r--  1 root root 3713946 Feb 16  2017 DynamoDBLocal.jar
   4 drwxr-xr-x  2 root root    4096 Feb  4 17:55 DynamoDBLocal_lib
  12 -rw-r--r--  1 root root    8644 Feb 16  2017 LICENSE.txt
   4 -rw-r--r--  1 root root     795 Feb 16  2017 README.txt
   4 drwxr-xr-x  2 root root    4096 Feb  4 17:55 third_party_licenses
Start DynamoDB
Start Dynamo
To start DynamoDb, you need to be sure you are in the directory listed above, and then issue the following command
$ java -Djava.library.path=./DynamoDBLocal_lib -jar DynamoDBLocal.jar -sharedDb
Initializing DynamoDB Local with the following configuration:
Port:   8000
InMemory:       false
DbPath: null
SharedDb:       true
shouldDelayTransientStatuses:   false
CorsParams:     *
To check it is running ok, point a browser at {your IP address}:8000/shell/ and you should see the shell as shown above.
Create a Local DynamoDb Database
Once DynamoDb is up and running, you could write some code to create a database. However it is much easier to use the aws command line. All the options I list below are mandatory. I decided to define an attribute named id which I will generate when I write records.
$ aws dynamodb create-table --table-name=vote --attribute-definitions AttributeName=id,AttributeType=S --key-schema AttributeName=id,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5  --endpoint-url http://localhost:8000
{
    "TableDescription": {
        "TableArn": "arn:aws:dynamodb:ddblocal:000000000000:table/vote", 
        "AttributeDefinitions": [
            {
                "AttributeName": "id", 
                "AttributeType": "S"
            }
        ], 
        "ProvisionedThroughput": {
            "NumberOfDecreasesToday": 0, 
            "WriteCapacityUnits": 5, 
            "LastIncreaseDateTime": 0.0, 
            "ReadCapacityUnits": 5, 
            "LastDecreaseDateTime": 0.0
        }, 
        "TableSizeBytes": 0, 
        "TableName": "vote", 
        "TableStatus": "ACTIVE", 
        "KeySchema": [
            {
                "KeyType": "HASH", 
                "AttributeName": "id"
            }
        ], 
        "ItemCount": 0, 
        "CreationDateTime": 1517770607.687
    }
}
Let's double check everything is ok
$ aws dynamodb list-tables --endpoint-url http://localhost:8000
{
    "TableNames": [
        "vote"
    ]
}