Exploring Daemon Sets and Cron Jobs

Janakiram MSVAnalyst | Advisor | ArchitectJanakiram & AssociatesGoogle Developer Expert

@janakiramm

Objectives

● Recap of Kubernetes Controllers● What are Daemon Sets?● Daemon Sets vs. Replica Sets● Use Cases for Daemon Sets● Configuring Run to Completion Jobs● Scheduling Jobs with Cron

Kubernetes Controllers

● Replica Sets● Deployments● Stateful Sets● Daemon Sets● Jobs (One time)● Cron Jobs

Overview of Daemon Set

● Daemon Set runs a copy of a pod on every node in a Kubernetes cluster

● Daemon Set and Replica Set are similar but have different use cases● New nodes automatically gets a Daemon Set pod● When a node is removed, the Daemon Set pod will not be rescheduled

Total number of pods in the Daemon Set == The number of nodes in cluster

Daemon Set vs Replica Set

Replica SetCount = 6

P1

P2

P3

P4

P5

P6

Node 1 Node 2 Node 3

Replica Set

Daemon Set vs Replica Set

Daemon Set

P1 P2 P3

Node 1 Node 2 Node 3

Daemon Set

Daemon Set Use Cases

● Logging Aggregators● Monitoring● Load Balancers / Reverse Proxies / API Gateways● Generic background job that needs to be run on each

node

DemoExploring Daemon Set

Jobs in Kubernetes

● There are two types of job controllers in Kubernetes○ One time / Run on completion○ Scheduled Jobs

● Both are extremely useful in performing batch operations● Jobs complement other controllers like Replica Set and

Daemon Set

Run to Completion Jobs

● Each Job creates one or more pods and ensures that they are successfully terminated

● If a pod or node fails during the execution, job controller will restart or reschedules the pod

● Job can also be used to run multiple pods in parallel● A job can be scaled up using the kubectl scale command● Job’s spec may define the parallelism value for running multiple pods in

parallel

Use case for Jobs

● One time, initialization of resources○ Databases○ File Systems○ Cache○ Configuration

● Multiple workers to process messages in a queue

DemoUsing Run to Complete Jobs

Configuring Cron Jobs

● A Cron Job manages time based Jobs○ Once at a specified point in time○ Repeatedly at a specified point in time

● Each Cron Job is similar to one line of a crontab (cron table) file● A typical use cases include

○ Schedule a job execution at a given point in time.○ Create a periodic job

■ Database backup■ Sending emails

Works only on clusters with --runtime-config=batch/v2alpha1=true

DemoUsing Cron Jobs

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