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DREAMaaS Middleware SDK

This SDK allows experimenting with the DREAMaaS API on a cluster.

1.Setup

We assume a linux machine with a recent distribution.

Prerequisites: Java 7, git, maven3 (For Ubuntu, see https://launchpad.net/~natecarlson/+archive/maven3. The command will be then 'mvn3' instead of 'mvn'.)

1.1. Installing Cassandra 1.2

We use the datastax packages for cassandra. For instructions, see http://www.datastax.com/docs/1.2/install/index For red-hat like systems, as root, do

cat > /etc/yum.repos.d/datastax.repo <<EOF
[datastax]
name= DataStax Repo for Apache Cassandra
baseurl=http://rpm.datastax.com/community
enabled=1
gpgcheck=0
EOF

yum install cassandra12
systemctl start cassandra.service

to make sure cassandra start at boot

systemctl enable cassandra.service

to see if it runs correctly

systemctl status cassandra.service

The distributed version requires a cluster of at least three Cassandra servers

1.2. Installing the DREAMaaS SDK

The sdk can be cloned from github (https://github.com/dreamaas). The repository is called taskworker-core. Checking out the repository and compiling the code can be done with the following commands:

git clone git://github.com/dreamaas/taskworker-core.git
cd taskworker-core
mvn clean install

This generates a jar in the target directory with all dependencies included.

The mvn install command also installs the generated artifacts in your local repository.

In target a tar.bz2 file of the project is created, in conjunction with the spec file in the root, an rpm file can be created for recent fedora versions:

cp target/taskworker-core.tar.bz2 ~/rpmbuild/SOURCES/
rpmbuild -bb taskworker-core.spec

For a manual install:

  • Copy the generated jar to /usr/share/java

    cp target/taskworker-core.jar /usr/share/java

  • Copy the two executable scripts to /usr/bin or /usr/local/bin

    cp bin/taskworker-server bin/taskworker-client /usr/bin

  • Create the configuration directory

    mkdir /etc/taskworker

  • Properties can be overridden by defining them in /etc/taskworker/config.properties

Note: In the taskworker-server script the location of the properties file and the jar can be changed.

1.3 Starting taskworker server and execute a workflow

The taskworker-workers repository contains the code for several workers and integration projects that generate jar with all the worker code and have a configuration file that defines the workers, the schedular config and the workflows.

The /etc/taskworker/config.properties properties file should define the location of the workflow configuration file (yaml file format) in the property taskworker.configfile

The properties file determines which components of the server are started:

  • workers: The workers defined and used the workflows

  • scheduler: A scheduler that starts jobs by moving them onto the work queue. Only one scheduler per "cluster" must be started.

  • rest: A rest interface to submit jobs and track their progress.

By default the middleware starts a non-distributed version which uses local locking only. In a distributed setting the workers need at least 3 cassandra instances to ensure quorum is achieved when a lock is requested. To start the distirbutedment version set taskworker.distributed property to true.

The taskworker-client script is a Python script that uses the built-in REST interface to interact with the taskworker-server.