Borg System Architecture

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Questions and Answers

What happens to a Borglet if it does not respond to several poll messages?

  • It restarts automatically
  • It is marked as down and tasks are rescheduled on other machines (correct)
  • It loses all its data
  • It is marked as up and continues to run tasks

What is the primary function of the Fauxmaster?

  • To debug failures by interacting with a simulated Borgmaster (correct)
  • To manage state machines for objects in the system
  • To schedule tasks in a Borg cell
  • To handle client RPCs in a Borg cell

What is the primary function of the Borgmaster?

  • To communicate with other Borgmasters
  • To run tasks and services on Borglets
  • To manage and schedule tasks on Borglets (correct)
  • To store tasks and services

How do scheduler replicas operate in a cell?

<p>They operate on a cached copy of the cell state (C)</p>
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How many replicas of the Borgmaster are there in a cell?

<p>Five (A)</p>
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What is the minimum number of CPU cores required to run a busy Borgmaster?

<p>10-14 CPU cores (D)</p>
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What is the role of the Borglet in a Borg cell?

<p>To run on each machine in a cell (C)</p>
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What is the function of the scheduler in a Borg cell?

<p>To schedule tasks and allocate resources (D)</p>
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What is the maximum number of machines a single Borgmaster can manage in a cell?

<p>Thousands of machines (B)</p>
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What happens to tasks on a Borglet if the Borgmaster fails?

<p>Tasks continue to run normally (C)</p>
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What is the purpose of the main Borgmaster process?

<p>To handle client RPCs and provide read-only access to data (B)</p>
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What is the role of the Borgmaster in a Borg cell?

<p>To manage state machines for all objects and communicate with Borglets (B)</p>
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What is the purpose of a Chubby lock in the Borgmaster election process?

<p>To allow other systems to find the newly elected master (C)</p>
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What happens when a replica recovers from an outage in the Paxos-based store?

<p>It dynamically re-synchronizes its state from other Paxos replicas (C)</p>
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What is the purpose of a checkpoint in the Borgmaster's state?

<p>All of the above (D)</p>
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What is the typical time it takes to elect a new master and failover to it in a small cell?

<p>10 seconds (D)</p>
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What is the purpose of Fauxmaster, a high-fidelity Borgmaster simulator?

<p>To read checkpoint files (C)</p>
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What is the benefit of the Borgmaster's features for SREs?

<p>They allow SREs to manage a few tens of thousands of machines per person (C)</p>
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Flashcards

Borglet non-response?

Marked as down, tasks rescheduled.

Fauxmaster's function?

Debug failures by interacting with a simulated Borgmaster.

Borgmaster's function?

Manage and schedule tasks on Borglets.

Scheduler replica operation?

Operate on a cached copy of the cell state.

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Borgmaster replicas?

Five

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Borgmaster CPU cores?

10-14 CPU cores

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Role of the Borglet?

To run on each machine in a cell

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Scheduler function?

Schedule tasks and allocate resources.

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Borgmaster scale?

Thousands of machines

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Tasks after Borgmaster fails?

Tasks continue to run normally.

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Main Borgmaster process?

Handle client RPCs and provide read-only access to data

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Borgmaster's role?

Manage state machines for all objects and communicate with Borglets

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Chubby lock purpose?

To allow other systems to find the newly elected master.

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Replica recovery?

It dynamically re-synchronizes its state from other Paxos replicas.

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Checkpoint?

All of the above

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Master election time?

10 seconds

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Fauxmaster purpose?

To read checkpoint files

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Borgmaster's benefit?

They allow SREs to manage a few tens of thousands of machines per person

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Study Notes

Borg System

  • A Borglet is marked as down if it doesn't respond to several poll messages, and its tasks are rescheduled on other machines.
  • When communication is restored, the Borgmaster instructs the Borglet to kill rescheduled tasks to prevent duplicates.

Borgmaster Architecture

  • A Borgmaster consists of two processes: the main Borgmaster process and a separate scheduler.
  • The main Borgmaster process handles client RPCs, manages state machines, communicates with Borglets, and provides a web UI.
  • The scheduler is responsible for scheduling tasks and operates on a cached copy of the cell state.

Scalability

  • A single Borgmaster can manage thousands of machines in a cell, with arrival rates above 10,000 tasks per minute.
  • A busy Borgmaster uses 10-14 CPU cores and up to 50 GiB RAM.

Borg Architecture

  • A Borg cell consists of a set of machines, a Borgmaster, and an agent process called the Borglet that runs on each machine.
  • All components of Borg are written in C++.

Borglet Operation

  • A Borglet continues normal operation even if it loses contact with the Borgmaster, ensuring currently running tasks and services remain up.

Fauxmaster

  • Fauxmaster is a high-fidelity Borgmaster simulator that can read checkpoint files and contains a complete copy of the production Borgmaster code.
  • It is useful for capacity planning, sanity checks, and debugging failures.

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