mistobaan / pfs Goto Github PK

Pfs is a distributed file system built specifically for the Docker ecosystem. You deploy it with Docker, just like other applications in your stack. Furthermore, MapReduce jobs are specified as Docker containers, rather than .jars, letting you perform distributed computation using any tools you want.

• Fault-tolerant architecture built on CoreOS
• Git-like distributed file system
• Dockerized MapReduce

No, pfs is at Alpha status. We'd love your help. :)

Pachyderm will eventually be a complete replacement for Hadoop, built on top of a modern toolchain instead of the JVM. Hadoop is a mature ecosystem, so there's a long way to go before pfs will fully match its feature set. However, thanks to innovative tools like btrfs, Docker, and CoreOS, we can build an order of magnitude more functionality with much less code.

Pfs is implemented as a distributed layer on top of btrfs, the same copy-on-write file system that powers Docker. Btrfs already offers git-like semantics on a single machine; pfs scales these out to an entire cluster. This allows features such as:

• Commit-based history: File systems are generally single-state entities. Pfs, on the other hand, provides a rich history of every previous state of your cluster. You can always revert to a prior commit in the event of a disaster.
• Branching: Thanks to btrfs's copy-on-write semantics, branching is ridiculously cheap in pfs. Each user can experiment freely in their own branch without impacting anyone else or the underlying data. Branches can easily be merged back in the main cluster.
• Cloning: Btrfs's send/receive functionality allows pfs to efficiently copy an entire cluster's worth of data while still maintaining its commit history.

The basic interface for MapReduce is a map function and a reduce function. In Hadoop this is exposed as a Java interface. In Pachyderm, MapReduce jobs are user-submitted Docker containers with http servers inside them. Rather than calling a map method on a class, Pachyderm POSTs files to the /map route on a webserver. This completely democratizes MapReduce by decoupling it from a single platform, such as the JVM.

Thanks to Docker, Pachyderm can seamlessly integrate external libraries. For example, suppose you want to perform computer vision on a large set of images. Creating this job is as simple as running npm install opencv inside a Docker container and creating a node.js server, which uses this library on its /map route.

# launch a local pfs shard
$ curl www.pachyderm.io/launch | sh
 
# clone the chess pipeline
$ git clone https://github.com/pachyderm/chess.git && cd chess
 
# install the pipeline locally and run it
$ install/pachyderm/local

####Step 1: Launch a local pfs shard Download and run the Pachyderm launch script to get a local instance running. ####Step 2: Clone the chess pipeline Clone the chess git repo we’ve provided. You can check out the full map code on GitHub. ####Step 3: Install the pipeline locally and run it Run the local install script to start the pipeline. It should take around 6 minutes.

Pfs is designed to run on CoreOS. To start, you'll need a working CoreOS cluster. Here's links on how to set one up:

• Google Compute Engine (recommended)
• Amazon EC2
• Vagrant (requires setting up DNS)

SSH in to one of your new CoreOS machines.

$ wget pachyderm.io/deploy/1Node.tar.gz
$ tar -xvf 1Node.tar.gz
$ fleetctl start 1Node/*

The startup process takes a little while the first time you run it because each node has to pull a Docker image.

As of v0.4 pfs can leverage s3 as a source of data for MapReduce jobs. Pfs also uses s3 as the backend for its local Docker registry. To get s3 working you'll need to provide pfs with credentials by setting them in etcd like so:

etcdctl set /pfs/creds/AWS_ACCESS_KEY_ID <AWS_ACCESS_KEY_ID>
etcdctl set /pfs/creds/AWS_SECRET_ACCESS_KEY <AWS_SECRET_ACCESS_KEY>
etcdctl set /pfs/creds/IMAGE_BUCKET <IMAGE_BUCKET>

The easiest way to see what's going on in your cluster is to use list-units, this is what a healthy 1 Node cluster looks like.

UNIT                            MACHINE                         ACTIVE          SUB
announce-master-0-1.service     0b0625cf.../172.31.9.86         active          running
announce-registry.service       0e7cf611.../172.31.27.115       active          running
gitdaemon.service               0b0625cf.../172.31.9.86         active          running
gitdaemon.service               0e7cf611.../172.31.27.115       active          running
gitdaemon.service               ed618559.../172.31.9.87         active          running
master-0-1.service              0b0625cf.../172.31.9.86         active          running
registry.service                0e7cf611.../172.31.27.115       active          running
router.service                  0b0625cf.../172.31.9.86         active          running
router.service                  0e7cf611.../172.31.27.115       active          running
router.service                  ed618559.../172.31.9.87         active          running

If you startup a new cluster and registry.service fails to start it's probably an issue with s3 credentials. See the section above.

Pfs exposes a git-like interface to the file system:

# Write <file> to <branch>. Branch defaults to "master".
$ curl -XPOST pfs/file/<file>?branch=<branch> -T local_file

# Read <file> from <master>.
$ curl pfs/file/<file>

# Read all files in a <directory>.
$ curl pfs/file/<directory>/*

# Read <file> from <commit>.
$ curl pfs/file/<file>?commit=<commit>

# Delete <file> from <branch>. Branch defaults to "master".
$ curl -XDELETE pfs/file/<file>?branch=<branch>

# Commit dirty changes to <branch>. Defaults to "master".
$ curl -XPOST pfs/commit?branch=<branch>

# Getting all commits.
$ curl -XGET pfs/commit

# Create <branch> from <commit>.
$ curl -XPOST pfs/branch?commit=<commit>&branch=<branch>

# Commit to <branch>
$ curl -XPOST pfs/commit?branch=<branch>

# Getting all branches.
$ curl -XGET pfs/branch

###MapReduce

####Creating a new job descriptor

Jobs are specified as JSON files in the following format:

{
    "type"  : either "map" or "reduce"
    "input" : a directory in pfs, S3 URL, or the output from another job
    "image" : the Docker image to use 
    "command" : the command to start your web server
}

NOTE: You do not need to specify the output location for a job. The output of a job, often referred to as a materialized view, is automatically stored in pfs /job/<jobname>.

####POSTing a job to pfs

Post a local JSON file with the above format to pfs:

$ curl -XPOST <host>/job/<jobname> -T <localfile>.json

NOTE: POSTing a job doesn't run the job. It just records the specification of the job in pfs.

####Running a job Jobs are only run on a commit. That way you always know exactly the state of the file system that is used in a computation. To run all committed jobs, use the commit keyword with the run parameter.

$ curl -XPOST <host>/commit?run

Think of adding jobs as constructing a DAG of computations that you want performed. When you call /commit?run, Pachyderm automatically schedules the jobs such that a job isn't run until the jobs it depends on have completed.

####Getting the output of a job Each job records its output in its own read-only file system. You can read the output of the job with:

$ curl <host>/job/<jobname>/file/*?commit=<commit>

or get just a specific file with:

$ curl -XGET <host>/job/<job>/file/*?commit=<commit>

NOTE: You must specify the commit you want to read from and that commit needs to have been created with the run parameter. We're planning to expand this API to make it not have this requirement in the near future. ####Creating a job:

# Delete <job>
$ curl -XDELETE <host>/job/<job>

# Read <job>
$ curl -XGET <host>/job/<job>

Two guys who love data and communities and both happen to be named Joe. We'd love to chat: [email protected] [email protected].

We're hiring! If you like ambitious distributed systems problems and think there should be a better alternative to Hadoop, please reach out. Email [email protected]

Want to hack on pfs for fun? You can run pfs locally using:

scripts/dev-launch

This will build a docker image from the working directory, tag it as pfs and launch it locally using scripts/launch. The only dependencies are Docker >= 1.5 and btrfs-tools >= 3.14. The script checks for this and gives you directions on how to fix it.