Paradrop: Enabling Lightweight Multi-tenancy at the Network’s Extreme Edge

Summary
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The paper motivates the need for edge computing platforms by pointing out the drawbacks of the existing cloud computing platform - high latency, lower responsiveness, lower availability, and privacy concerns. To solve these, it introduces a flexible edge computing platform, Paradrop, that allows third-party developers to create and deploy services using the computing and storage resources at the extreme edge of the network, WiFi Access Points (AP) or other wireless gateways. WiFi AP's proximity to the end devices helps achieve low latency and higher responsiveness. It is always on and thus, available. Paradrop's ability to store sensitive data locally, and not send it to a cloud service over the open internet, helps ensure privacy.
The paper discusses 3 key components of the platform -
1) A flexible virtualization hosting substrate present in the WiFi APs to provide isolated environment to services running on the AP. The paper refers to these isolated containers as chutes. It tries to maximize the of resources' usage for services by using more efficient virtualization technology based on Linux containers rather than Virtual Machines.
2) A cloud-based backend which manages all the resources of the Paradrop platform in a centralized manner, and provides API for the developers to deploy chutes on the APs.
3) APIs to deploy and manage chutes across different Paradrop APs. Paradrop backend uses WAMP (Web Application Messaging Protocol) to communicate with all the APs to dispatch commands and receive respones. Paradrop backend uses HTTP RESTful APIs to visualize the aggregated information from all the APs.

Strengths
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1) In addition to explaining the framework, the paper also presents two example applications in detail - Security camera service and Environemntal sensor service using Paradrop. This is very helpful both for new users and developers to adopt the platform.
2) Since, virtualization is the core of the Paradrop platform, the authors provide details about the experiments involved in implementation of three different generations of virtualization schemes, and also reasons to accept/reject each one of them. The explainations provided can easily be used when trying to decide a virtualization scheme in some other context.
3) The framework has been designed and implemented with developer in focus, and they provide a fully featured API for development making it easy for developers to have complete control over the configuration of their chutes.
4) The paper identifies problems, and provides a lot of useful ideas about future work -
        i) A strategy based on "share" value can be implemented for network sharing between the chutes as opposed to the current method of restricting speed by traffic shaping.
       ii) To provide a flexible way to manage the limited storage resources in the gateways, policies like disk size quota for a chute, can be implemented to manage the block devices based on Linux kernel’s device mapper and Docker’s “devicemapper” storage driver.
   
Weaknesses
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1) Currently the chute package should be available locally for the Paradrop developer console if a user wants to deploy a chute to an AP.
2) Since, Docker is an App-container, it is suitable for single process chutes only. Also, use of containers (Docker) for virtualization forces the deveopers to manage networking environment by themselves.
3) The present configurations allow to define a common maximum disk size for all chutes. The flexibility to define different disk sizes for different chutes is listed as future work.
4) As Paradrop backend uses WAMP to communicate with all the APs, WAMP message router may be a bottleneck in case of large number of APs.

Discussion Points
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1) Effect on Wifi APs capacity to handle networking load when acting as computing platform.
2) What if an AP is shut down / crashes in the middle of computation ?


For additional information related to Paradrop -
[1] https://www.paradrop.org/
[2] https://www.youtube.com/watch?v=yyuM7W-HjQo