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Amazon DynamoDB Persistence

This service allows you to persist state updates using the Amazon DynamoDB database. Query functionality is also fully supported.

Features:

  • Writing/reading information to relational database systems
  • Configurable database table names
  • Automatic table creation

Disclaimer

This service is provided “AS IS”, and the user takes full responsibility of any charges or damage to Amazon data.

Table of Contents

Prerequisites

You must first set up an Amazon account as described below.

Users are recommended to familiarize themselves with AWS pricing before using this service. Please note that there might be charges from Amazon when using this service to query/store data to DynamoDB. See Amazon DynamoDB pricing pages for more details. Please also note possible Free Tier benefits.

Setting Up an Amazon Account

  • Sign up for Amazon AWS.
  • Select the AWS region in the AWS console using these instructions. Note the region identifier in the URL (e.g. https://eu-west-1.console.aws.amazon.com/console/home?region=eu-west-1 means that region id is eu-west-1).
  • Create user for openHAB with IAM
    • Open Services -> IAM -> Users -> Create new Users. Enter openhab to User names, keep Generate an access key for each user checked, and finally click Create.
    • Show User Security Credentials and record the keys displayed
  • Configure user policy to have access for dynamodb
    • Open Services -> IAM -> Policies
    • Check AmazonDynamoDBFullAccess and click Policy actions -> Attach
    • Check the user created in step 2 and click Attach policy

Configuration

This service can be configured in the file services/dynamodb.cfg.

Basic configuration

Property Default Required Description
accessKey   Yes access key as shown in Setting up Amazon account.
secretKey   Yes secret key as shown in Setting up Amazon account.
region   Yes AWS region ID as described in Setting up Amazon account. The region needs to match the region that was used to create the user.

Configuration Using Credentials File

Alternatively, instead of specifying accessKey and secretKey, one can configure a configuration profile file.

Property Default Required Description
profilesConfigFile   Yes path to the credentials file. For example, /etc/openhab2/aws_creds. Please note that the user that runs openHAB must have approriate read rights to the credential file. For more details on the Amazon credential file format, see Amazon documentation.
profile   Yes name of the profile to use
region   Yes AWS region ID as described in Step 2 in Setting up Amazon account. The region needs to match the region that was used to create the user.

Example of service configuration file (services/dynamodb.cfg):

profilesConfigFile=/etc/openhab2/aws_creds
profile=fooprofile
region=eu-west-1

Example of credentials file (/etc/openhab2/aws_creds):

[fooprofile]
aws_access_key_id=testAccessKey
aws_secret_access_key=testSecretKey

Advanced Configuration

In addition to the configuration properties above, the following are also available:

Property Default Required Description
readCapacityUnits 1 No read capacity for the created tables
writeCapacityUnits 1 No write capacity for the created tables
tablePrefix openhab- No table prefix used in the name of created tables

Refer to Amazon documentation on provisioned throughput for details on read/write capacity.

All item- and event-related configuration is done in the file persistence/dynamodb.persist.

Details

Tables Creation

When an item is persisted via this service, a table is created (if necessary). Currently, the service will create at most two tables for different item types. The tables will be named <prefix><item-type>, where <prefix> matches the tablePrefix configuration property; while the <item-type> is either bigdecimal (numeric items) or string (string and complex items).

Each table will have three columns: itemname (item name), timeutc (in ISO 8601 format with millisecond accuracy), and itemstate (either a number or string representing item state).

Caveats

When the tables are created, the read/write capacity is configured according to configuration. However, the service does not modify the capacity of existing tables. As a workaround, you can modify the read/write capacity of existing tables using the Amazon console.

Developer Notes

Updating Amazon SDK

  1. Clean lib/*
  2. Update SDK version in scripts/fetch_sdk_pom.xml. You can use the maven online repository browser to find the latest version available online.
  3. scripts/fetch_sdk.sh
  4. Copy scripts/target/site/dependencies.html and scripts/target/dependency/*.jar to lib/
  5. Generate build.properties entries ls lib/*.jar | python -c "import sys; print(' ' + ',\\\\\\n '.join(map(str.strip, sys.stdin.readlines())))"
  6. Generate META-INF/MANIFEST.MF Bundle-ClassPath entries ls lib/*.jar | python -c "import sys; print(' ' + ',\\n '.join(map(str.strip, sys.stdin.readlines())))"
  7. Generate .classpath entries ls lib/*.jar | python -c "import sys;pre='<classpathentry exported=\"true\" kind=\"lib\" path=\"';post='\"/>'; print('\\t' + pre + (post + '\\n\\t' + pre).join(map(str.strip, sys.stdin.readlines())) + post)"