PLuSH

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PLuSH Mesh Tree

• Fast and Robust Wide-Area Remote Execution

Mikhail Afanasyev ? Jose Garcia ? Brian Lum
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Introduction

• PlanetLab is an open platform for developing,
  deploying and accessing planetary-scale services
• It allows remote execution on nodes around the
  world
• Extremely useful in developing new network
  technologies

Introduction ? Mesh Tree ? Additional
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PlanetLab

• Current distribution of 534 nodes over 253 sites

Introduction ? Mesh Tree ? Additional
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The Motivation

• Performance is abysmal
• Currently, the user must make an SSH connection
  to each node
• As the number of nodes grows, the overhead of
  establishing SSH connections becomes more
  significant
• Not all nodes can reach one another directly

Introduction ? Mesh Tree ? Additional
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The Motivation

• Flaky Control
• Controlling large sets of remote processes is
  difficult
• Example C-c will result in remote processes
  being killed or straggler processors to remain

Introduction ? Mesh Tree ? Additional
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PLuSH

• Suppose that someone wants to test a new network
  application and decides to run the code on 100
  machines
• First, we must be able to determine a list of
  target nodes to run the experience. Nodes can be
  picked depending on factors including CPU load,
  bandwidth, latency, etc.
• Next, the code must be deployed
• The code must be started simultaneously on all
  machines.
• Once the code is running, we must be able monitor
  the progress and collect statistics

Introduction ? Mesh Tree ? Additional
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PLuSH

• One of the core parts of Plush is the Mesh
  interface
• Mesh abstracts the underlying overlay
• Mesh uses a rough list of hosts to construct an
  overlay communication mesh by using the host
  directory to query host names and authentication
  information.

Introduction ? Mesh Tree ? Additional
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Weaving the Mesh

• SSH authentication forwarding
• Building the tree
• Adding robustness

Mesh Tree SSH Forwarding ? Building the Tree ?
Robustness
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How SSH Works

• Agent listens on agent socket which is a Unix
  domain socket. Agent has private key.
• SSH (on agents side) makes a connection from
  Home PC to SSHd (daemon) on PL1, who has the
  public key.
• SSHd sends challenge to SSH. SSH connects to
  Agent socket, gives challenge to Agent. Agent
  uses private key to make response and forwards to
  SSH, who forwards to SSHd.

Mesh Tree SSH Forwarding ?Building the Tree ?
Robustness
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Our World with PlanetLab
Home PC
PL1
PL2
Slice 0
Slice UCSD
Agent
private key
Challenge
Response
Challenge
Challenge
SSH
SSHd
SSH
SSHd
public key
public key
Response
The slice breaks up PL1, so SSH cannot forward to
SSHd
Mesh Tree SSH Forwarding ?Building the Tree ?
Robustness
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Our Solution
Home PC
PL1
PL2
Slice 0
Slice UCSD
Agent
private key
Client
Challenge
SSH Mesh Response
SSH Mesh Challenge
Response
Response
Challenge
Challenge
Challenge
SSH
SSHd
SSH
SSHd
public key
public key
Response
Response
Clients STDIN and STDOUT are connected to SSHd
Mesh Tree SSH Forwarding ?Building the Tree ?
Robustness
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Building the Tree

• There is rudimentary support for a tree
• We implemented multiple tree-building algorithms
• Trees can be built using SSH tree and Macedon

Mesh Tree SSH Forwarding? Building the Tree ?
Robustness
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Macedon vs. SSH Mesh

• Macedon
• Advantages
• Support for many protocols
• Does not spend time decrypting and encrypting
• Disadvantages
• Can be easily hijacked
• Heavy program

• SSH Mesh
• Advantages
• Requires minimum client software
• Provides protection against both sniffing and
  hijacking
• Disadvantages
• Spends time decrypting and encrypting

Mesh Tree SSH Forwarding? Building the Tree ?
Robustness
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Adding Robustness

• The Forwarding mechanism
• Forwards SSH connection
• Allows us to change root so that we can detach
  the experiment controller
• Allows us to recover from failures in the root

Mesh Tree SSH Forwarding ? Building the Tree ?
Robustness
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Comparing the trees
Introduction ? Mesh Tree ? Additional
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Additional Tools

• Debugging Tool
• Deploys required files to all necessary nodes
• Opens multiple simultaneous connections for very
  high speeds
• Stops runaway processes
• Macedon Testing Tool
• Shows raw data for underlying Macedon
  communication networks
• Controls Macedon networks from console
• Uses self-developed Perl Macedon bindings

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Future Research Work

• Comparison between more Mesh overlay algorithms
• Evaluate the performance difference between SSH
  Mesh and Macedon

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Additional Thanks

• We would like to thank the following people for
  their help
• Chris Tuttle
• Jeannie Albrecht
• Chip Killian

Introduction ? Mesh Tree ? Additional
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Conclusion

• Remote execution in PlanetLab through basic SSH
  connections is neither scalable nor robust
• We have implemented a solution that improves both
  scalability and robustness
• SSH forwarding mechanism
• Building the tree
• Adding robustness

Introduction ? Mesh Tree ? Additional