Amazon DynamoDB Storage Backend for JanusGraph

JanusGraph: Distributed Graph Database is a scalable graph database optimized for storing and querying graphs containing hundreds of billions of vertices and edges distributed across a multi-machine cluster. JanusGraph is a transactional database that can support thousands of concurrent users executing complex graph traversals in real time. -- JanusGraph Homepage

Amazon DynamoDB is a fast and flexible NoSQL database service for all applications that need consistent, single-digit millisecond latency at any scale. It is a fully managed database and supports both document and key-value data models. Its flexible data model and reliable performance make it a great fit for mobile, web, gaming, ad-tech, IoT, and many other applications. -- AWS DynamoDB Homepage

JanusGraph + DynamoDB = Distributed Graph Database - Cluster Host Management

Features

The following is a list of features of the Amazon DynamoDB Storage Backend for JanusGraph.

• AWS managed authentication and authorization.
• Configure table prefix to allow multiple graphs to be stored in a single account in the same region.
• Full graph traversals with rate limited table scans.
• Flexible data model allows configuration between single-item and multiple-item model based on graph size and utilization.
• Test graph locally with DynamoDB Local.
• Integrated with JanusGraph metrics.
• JanusGraph 0.2.0 and TinkerPop 3.2.6 compatibility.
• Upgrade compatibility from Titan 1.0.0.

Getting Started

This example populates a JanusGraph database backed by DynamoDB Local using the Marvel Universe Social Graph. The graph has a vertex per comic book character with an edge to each of the comic books in which they appeared.

Load a subset of the Marvel Universe Social Graph

1. Install the prerequisites (Git, JDK 1.8, Maven, Docker, wget, gpg) of this tutorial. The command below uses a convenience script for Amazon Linux on EC2 instances to install Git, Open JDK 1.8, Maven, Docker and Docker Compose. It adds the ec2-user to the docker group so that you can execute Docker commands without using sudo. Log out and back in to effect changes on ec2-user.

   curl https://raw.githubusercontent.com/awslabs/dynamodb-janusgraph-storage-backend/master/src/test/resources/install-reqs.sh | bash
   exit

2. Clone the repository and change directories.

   git clone https://github.com/awslabs/dynamodb-janusgraph-storage-backend.git && cd dynamodb-janusgraph-storage-backend

3. Use Docker and Docker Compose to bake DynamoDB Local into a container and start Gremlin Server with the DynamoDB Storage Backend for JanusGraph installed.

   docker build -t awslabs/dynamodblocal ./src/test/resources/dynamodb-local-docker \
   && src/test/resources/install-gremlin-server.sh \
   && cp server/dynamodb-janusgraph-storage-backend-*.zip src/test/resources/dynamodb-janusgraph-docker \
   && mvn docker:build -Pdynamodb-janusgraph-docker \
   && docker-compose -f src/test/resources/docker-compose.yml up -d \
   && docker exec -i -t dynamodb-janusgraph /var/jg/bin/gremlin.sh

4. After the Gremlin shell starts, set it up to execute commands remotely.

   :remote connect tinkerpop.server conf/remote.yaml session
   :remote console

5. Load the first 100 lines of the Marvel graph using the Gremlin shell.

   com.amazon.janusgraph.example.MarvelGraphFactory.load(graph, 100, false)

6. Print the characters and the comic-books they appeared in where the characters had a weapon that was a shield or claws.

   g.V().has('weapon', within('shield','claws')).as('weapon', 'character', 'book').select('weapon', 'character','book').by('weapon').by('character').by(__.out('appeared').values('comic-book'))

7. Print the characters and the comic-books they appeared in where the characters had a weapon that was not a shield or claws.

   g.V().has('weapon').has('weapon', without('shield','claws')).as('weapon', 'character', 'book').select('weapon', 'character','book').by('weapon').by('character').by(__.out('appeared').values('comic-book'))

8. Print a sorted list of the characters that appear in comic-book AVF 4.

   g.V().has('comic-book', 'AVF 4').in('appeared').values('character').order()

9. Print a sorted list of the characters that appear in comic-book AVF 4 that have a weapon that is not a shield or claws.

   g.V().has('comic-book', 'AVF 4').in('appeared').has('weapon', without('shield','claws')).values('character').order()

10. Exit remote mode and Control-C to quit.

    :remote console

11. Clean up the composed Docker containers.

    docker-compose -f src/test/resources/docker-compose.yml stop

Load the Graph of the Gods

1. Repeat steps 3 and 4 of the Marvel graph section, cleaning up the server directory beforehand with rm -rf server.

2. Load the Graph of the Gods.

   GraphOfTheGodsFactory.loadWithoutMixedIndex(graph, true)

3. Now you can follow the rest of the JanusGraph Getting Started documentation, starting from the Global Graph Indeces section. See the scriptEngines/gremlin-groovy/scripts list element in the Gremlin Server YAML file for more information about what is in scope in the remote environment.
4. Alternatively, repeat steps 1 through 8 of the Marvel graph section and follow the examples in the TinkerPop documentation. Skip the TinkerGraph.open() step as the remote execution environment already has a graph variable set up. TinkerPop have other tutorials available as well.

Run Gremlin on Gremlin Server in EC2 using CloudFormation templates

The DynamoDB Storage Backend for JanusGraph includes CloudFormation templates that creates a VPC, an EC2 instance in the VPC, installs Gremlin Server with the DynamoDB Storage Backend for JanusGraph installed, and starts the Gremlin Server Websocket endpoint. Also included are templates that create the graph's DynamoDB tables. The Network ACL of the VPC includes just enough access to allow:

• you to connect to the instance using SSH and create tunnels (SSH inbound)
• the EC2 instance to download yum updates from central repositories (HTTP outbound)
• the EC2 instance to download your dynamodb.properties file and the Gremlin Server package from S3 (HTTPS outbound)
• the EC2 instance to connect to DynamoDB (HTTPS outbound)
• the ephemeral ports required to support the data flow above, in each direction

Requirements for running this CloudFormation template include two items.

• You require an SSH key for EC2 instances must exist in the region you plan to create the Gremlin Server stack.
• You require permission to call the ec2:DescribeKeyPairs API when creating a stack from the AWS console.
• You need to have created an IAM role in the region that has S3 Read access and DynamoDB full access, the very minimum policies required to run this CloudFormation stack. S3 read access is required to provide the dynamodb.properties file to the stack in cloud-init. DynamoDB full access is required because the DynamoDB Storage Backend for JanusGraph can create and delete tables, and read and write data in those tables.

Note, this cloud formation template downloads the JanusGraph zip files available on the JanusGraph downloads page. The CloudFormation template downloads these packages and builds and adds the DynamoDB Storage Backend for JanusGraph with its dependencies.

CloudFormation Template table

Below you can find a list of CloudFormation templates discussed in this document, and links to launch each stack in CloudFormation and to view the stack in the designer.

Instructions to Launch CloudFormation Stacks

1. Choose between the single and multiple item data models and create your graph tables with the corresponding CloudFormation template above by downloading it and passing it to the CloudFormation console. Note, the configuration provided in src/test/resources/dynamodb.properties assumes that you will deploy the stack in us-west-2 and that you will use the multiple item model.
2. Inspect the latest version of the Gremlin Server on DynamoDB stack in the third row above.
3. Download the template from the third row to your computer and use it to create the Gremlin Server on DynamoDB stack.
4. On the Select Template page, name your Gremlin Server stack and select the CloudFormation template that you just downloaded.
5. On the Specify Parameters page, you need to specify the following:
   • EC2 Instance Type
   • The Gremlin Server port, default 8182.
   • The S3 URL to your dynamodb.properties configuration file
   • The name of your pre-existing EC2 SSH key. Be sure to chmod 400 on your key as EC2 instance will reject connections if permissions on the key are too open.
   • The network whitelist for the SSH protocol. You will need to allow incoming connections via SSH to enable the SSH tunnels that will secure Websockets connections to Gremlin Server.
   • The path to an IAM role that has the minimum amount of privileges to run this CloudFormation script and run Gremlin Server with the DynamoDB Storage Backend for JanusGraph. This role will require S3 read to get the dynamodb.properties file, and DynamoDB full access to create tables and read and write items in those tables. This IAM role needs to be created with a STS trust relationship including ec2.amazonaws.com as an identity provider. The easiest way to do this is to create a new role on the IAM console and from the AWS Service Role list in the accordion, select Amazon EC2, and add the AmazonDynamoDBFullAccess and AmazonS3ReadOnlyAccess managed policies.
6. On the Options page, click Next.
7. On the Review page, select "I acknowledge that this template might cause AWS CloudFormation to create IAM resources." Then, click Create.
8. Start the Gremlin console on the host through SSH. You can just copy paste the GremlinShell output of the CloudFormation template and run it on your command line.
9. Repeat steps 4 and onwards of the Marvel graph section above.

Data Model

The Amazon DynamoDB Storage Backend for JanusGraph has a flexible data model that allows clients to select the data model for each JanusGraph backend table. Clients can configure tables to use either a single-item model or a multiple-item model.

Single-Item Model

The single-item model uses a single DynamoDB item to store all values for a single key. In terms of JanusGraph backend implementations, the key becomes the DynamoDB hash key, and each column becomes an attribute name and the column value is stored in the respective attribute value.

This is definitely the most efficient implementation, but beware of the 400kb limit DynamoDB imposes on items. It is best to only use this on tables you are sure will not surpass the item size limit. Graphs with low vertex degree and low number of items per index can take advantage of this implementation.

Multiple-Item Model

The multiple-item model uses multiple DynamoDB items to store all values for a single key. In terms of JanusGraph backend implementations, the key becomes the DynamoDB hash key, and each column becomes the range key in its own item. The column values are stored in its own attribute.

The multiple item model is less efficient than the single-item during initial graph loads, but it gets around the 400kb limitation. The multiple-item model uses range Query calls instead of GetItem calls to get the necessary column values.

DynamoDB Specific Configuration

Each configuration option has a certain mutability level that governs whether and how it can be modified after the database is opened for the first time. The following listing describes the mutability levels.

1. FIXED - Once the database has been opened, these configuration options cannot be changed for the entire life of the database
2. GLOBAL_OFFLINE - These options can only be changed for the entire database cluster at once when all instances are shut down
3. GLOBAL - These options can only be changed globally across the entire database cluster
4. MASKABLE - These options are global but can be overwritten by a local configuration file
5. LOCAL - These options can only be provided through a local configuration file

Leading namespace names are shortened and sometimes spaces were inserted in long strings to make sure the tables below are formatted correctly.

General DynamoDB Configuration Parameters

All of the following parameters are in the storage (s) namespace, and most are in the storage.dynamodb (s.d) namespace subset.

DynamoDB KeyColumnValue Store Configuration Parameters

Some configurations require specifications for each of the JanusGraph backend Key-Column-Value stores. Here is a list of the default JanusGraph backend Key-Column-Value stores:

• edgestore
• graphindex
• janusgraph_ids (this used to be called titan_ids in Titan)
• system_properties
• systemlog
• txlog

Any store you define in the umbrella storage.dynamodb.stores.* namespace that starts with ulog_ will be used for user-defined transaction logs.

Again, if you opt out of storage-native locking with the storage.dynamodb.native-locking = false configuration, you will need to configure the data model, initial capacity and rate limiters for the three following stores:

• edgestorelock
• graphindexlock
• system_propertieslock

You can configure the initial read and write capacity, rate limits, scan limits and data model for each KCV graph store. You can always scale up and down the read and write capacity of your tables in the DynamoDB console. If you have a write once, read many workload, or you are running a bulk data load, it is useful to adjust the capacity of edgestore and graphindex tables as necessary in the DynamoDB console, and decreasing the allocated capacity and rate limiters afterwards.

For details about these Key-Column-Value stores, please see Store Mapping and JanusGraph Data Model. All of these configuration parameters are in the storage.dynamodb.stores (s.d.s) umbrella namespace subset. In the tables below these configurations have the text t where the JanusGraph store name should go.

When upgrading from Titan 1.0.0, you will need to set the ids.store-name configuration to titan_ids to avoid re-using id ranges that are already assigned.

DynamoDB Client Configuration Parameters

All of these configuration parameters are in the storage.dynamodb.client (s.d.c) namespace subset, and are related to the DynamoDB SDK client configuration.

DynamoDB Client Proxy Configuration Parameters

All of these configuration parameters are in the storage.dynamodb.client.proxy (s.d.c.p) namespace subset, and are related to the DynamoDB SDK client proxy configuration.

DynamoDB Client Socket Configuration Parameters

All of these configuration parameters are in the storage.dynamodb.client.socket (s.d.c.s) namespace subset, and are related to the DynamoDB SDK client socket configuration.

DynamoDB Client Executor Configuration Parameters

All of these configuration parameters are in the storage.dynamodb.client.executor (s.d.c.e) namespace subset, and are related to the DynamoDB SDK client executor / thread-pool configuration.

DynamoDB Client Credential Configuration Parameters

All of these configuration parameters are in the storage.dynamodb.client.credentials (s.d.c.c) namespace subset, and are related to the DynamoDB SDK client credential configuration.

Upgrading from Titan 1.0.0

Earlier versions of this software supported Titan 1.0.0. This software supports upgrading from the DynamoDB Storage Backend for Titan 1.0.0 by following the steps to update your configuration below.

1. Set the JanusGraph configuration option ids.store-name=titan_ids. This allows you to reuse your titan_ids table.
2. Update the classpath to the DynamoDB Storage Backend to use the latest package name, storage.backend=com.amazon.janusgraph.diskstorage.dynamodb.DynamoDBStoreManager .

Run all tests against DynamoDB Local on an EC2 Amazon Linux AMI

1. Install dependencies. For Amazon Linux:

   sudo wget http://repos.fedorapeople.org/repos/dchen/apache-maven/epel-apache-maven.repo \
     -O /etc/yum.repos.d/epel-apache-maven.repo
   sudo sed -i s/\$releasever/6/g /etc/yum.repos.d/epel-apache-maven.repo
   sudo yum update -y && sudo yum upgrade -y
   sudo yum install -y apache-maven sqlite-devel git java-1.8.0-openjdk-devel
   sudo alternatives --set java /usr/lib/jvm/jre-1.8.0-openjdk.x86_64/bin/java
   sudo alternatives --set javac /usr/lib/jvm/java-1.8.0-openjdk.x86_64/bin/javac
   git clone https://github.com/awslabs/dynamodb-janusgraph-storage-backend.git
   cd dynamodb-janusgraph-storage-backend && mvn install

2. Open a screen so that you can log out of the EC2 instance while running tests with screen.

3. Run the single-item data model tests.

   mvn verify -P integration-tests \
   -Dexclude.category=com.amazon.janusgraph.testcategory.MultipleItemTestCategory \
   -Dinclude.category="**/*.java" > o 2>&1

4. Run the multiple-item data model tests.

   mvn verify -P integration-tests \
   -Dexclude.category=com.amazon.janusgraph.testcategory.SingleItemTestCategory \
   -Dinclude.category="**/*.java" > o 2>&1

5. Run other miscellaneous tests.

   mvn verify -P integration-tests -Dinclude.category="**/*.java" \
       -Dgroups=com.amazon.janusgraph.testcategory.IsolateRemainingTestsCategory > o 2>&1

6. Exit the screen with CTRL-A D and logout of the EC2 instance.
7. Monitor the CPU usage of your EC2 instance in the EC2 console. The single-item tests may take at least 1 hour and the multiple-item tests may take at least 2 hours to run. When CPU usage goes to zero, that means the tests are done.

8. Log back into the EC2 instance and resume the screen with screen -r to review the test results.

   cd target/surefire-reports && grep testcase *.xml | grep -v "\/"

9. Terminate the instance when done.