Distributed Reliability: SRE Distributed Periodic Scheduling

SRE    |    Intermediate
  • 14 videos | 57m 34s
  • Includes Assessment
  • Earns a Badge
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Maintaining a distributed system requires constant maintenance to ensure failures don't interfere with that system's reliability and availability. Using periodic scheduling and replication, site reliability engineers can minimize the effect failures may have on a system's performance. One way to automate this process is to utilize the system daemon, cron. In this course, you'll explore how to use cron for task scheduling, the purpose, components, and operators involved in cron jobs, and the format and characters of cron syntax. You'll outline how cron works with distributed periodic scheduling and idempotency, and in largescale deployments. Next, you'll review the PAXOS distributed consensus algorithm, best practices for its use, and how it applies to distributed replication. Lastly, you'll practice scheduling a cron job and using cron syntax generators.


  • Discover the key concepts covered in this course
    Describe what is meant by cron and how to use it for scheduling jobs
    Outline the purpose of cron jobs, name their components and operators, and give examples of their use
    Describe the characteristics of the cron syntax and provide syntax examples
    Define the concept of idempotency and outline how distributed periodic scheduling works with cron
    Outline how to scale cron for large-scale system deployments
    Describe how the paxos distributed consensus algorithm works
  • Outline how replication is performed using the paxos algorithm
    Recognize best practices when using the paxos algorithm
    Describe how google approached building cron
    Outline how to perform distributed scheduling
    Demonstrate how to schedule cron jobs
    Illustrate how to use tools to generate crontab syntax
    Summarize the key concepts covered in this course


  • 1m 26s
  • 4m 53s
    In this video, you'll learn more about Cron. Cron is used to run tasks at designated times. These task executions are time triggered, so Cron is meant to execute background tasks. You'll learn cron files contain a list of commands to run at specified times. Each user has a crontab file, which is checked by the Cron daemon, even if they're not logged in. FREE ACCESS
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    3.  Cron Jobs
    3m 28s
    In this video, you'll learn more about Cron. This is a utility that can be used to schedule commands and scripts to run at specified dates and times. Cron jobs are especially useful for running repetitive tasks. You'll discover that there are three basic components of a cron job: the script, the command, and the output. The script will be executed when the cron jobs schedule triggers. The command will be what actually executes the script. And the output is the result of the script's action. FREE ACCESS
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    4.  Cron Syntax
    6m 36s
    In this video, you'll learn more about cron. You'll discover that programs, services, tasks, operating systems, and anything that needs background schedule-based triggering is best served using cron. You'll learn common examples include scheduling a cron job to execute long running scripts that don't require user intervention. FREE ACCESS
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    5.  Cron Jobs and Idempotency
    3m 34s
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    6.  Cron for Large-scale System Deployment
    5m 51s
    In this video, you'll learn how to outline how to scale cron for large-scale system deployments. You'll learn that when creating cron jobs, it's a good idea to keep a few different aspects in mind, such as maintaining idempotency. First, here are some examples of idempotent cron jobs that would need to be run on a distributed system. FREE ACCESS
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    7.  Paxos Distributed Consensus Algorithm
    3m 45s
    In this video, you'll learn about the Paxos algorithm for gaining distributed consensus. This operates as a sequence of proposals that are accepted or denied by a majority of the processes in the system. If accepted, the proposals are executed. The Paxos algorithm requires a majority vote from all the processes to reach consensus. FREE ACCESS
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    8.  Paxos Replication
    4m 19s
    In this video, you'll learn about stateful services on distributed systems that need to replicate their state data. Distributed systems must be able to quickly replicate state information on all relevant systems. When talking about replication, we're referring to storing multiple copies of data in multiple locations to ensure durability. FREE ACCESS
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    9.  Paxos Best Practices
    3m 41s
    In this video, you'll learn more about when to implement Paxos for distributed consensus. First, as a clear no-brainer, the consensus model needs to be fault tolerant and operational as long as most of the nodes are running. To get proper consensus and a quorum, multiple acceptors must be part of the system in order to decide on the proposed values. Once a proposed value is accepted by the majority of the acceptors, it's considered best practice that the value shouldn't change. FREE ACCESS
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    10.  Google Cron Example
    4m 56s
    Google has a process in place to manage Cron jobs on their distributed systems. Google uses Paxos to keep track of the state of each job, and also uses Paxos to notify participants when a cron job is about to start or finish. Cron jobs are idempotent, meaning that if one fails, the rest of the jobs will still run successfully. FREE ACCESS
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    11.  Distributed Scheduling
    4m 43s
    In this video, you'll learn how to outline how to perform distributed scheduling. You'll discover that with distributed scheduling, you can schedule a job on system one and two and then when that job is finished, you can schedule a job on system three. Distributed scheduling is handy when you have workflows to execute. FREE ACCESS
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    12.  Scheduling Cron Jobs
    3m 45s
    In this demonstration, you will learn how to schedule cron jobs in Unix. First, you will use crontab from the terminal to create two cron jobs that create files in a temp folder at different intervals. Then, you will open the crontab file and discover every job starts with the cron expression and then the command to issue. FREE ACCESS
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    13.  Using Cron Syntax Generators
    5m 27s
    In this video, you'll learn how to use tools to generate Crontab syntax. First, you'll use Crontab Guru to enter and validate a cron expression and see the human readable representation. Then you'll use Crontab generator to create an expression and review the times it would run.You'll also learn about the general format of a cron schedule. FREE ACCESS
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    14.  Course Summary
    1m 12s


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