Level Triggered and Reconciled: How Kubernetes Manages its State

@jrbowes Level-Triggered and Reconciled How Kubernetes Manages its State

@jrbowes @jrbowes Photo by Stefan Steinbauer on Unsplash STUDY TIME

@jrbowes https://www.manifold.co Say hi at our booth! James Bowes Technical
Lead

@jrbowes @jrbowes Photo by Maximilian Weisbecker on Unsplash KUBERNETES?

@jrbowes @jrbowes

@jrbowes @jrbowes Photo by Gamze Bozkaya on Unsplash THE CLIENT
API

@jrbowes @jrbowes

@jrbowes @jrbowes Photo by Jakob Owens on Unsplash PATCHING

@jrbowes JSON Merge Patch • Plain JSON document only containing
changes • Declarative and simple • RFC 7386

@jrbowes JSON Merge Patch ... metadata: labels: service: worker app:
marketplace spec: containers: - image: manifold/worker:1.31.18 name: worker

@jrbowes JSON Merge Patch metadata: labels: service: billing-worker spec: containers:
- image: manifold/sidecar:1.0.0 name: metrics

@jrbowes JSON Merge Patch ... metadata: labels: service: billing-worker app:
marketplace spec: containers: - image: manifold/sidecar:1.0.0 name: metrics

@jrbowes JSON Merge Patch • Objects are always merged •
Arrays are always replaced • No explicit null See also JSON Patch (RFC 6902) - Verbose and complex

@jrbowes Strategic Merge Patch • Adds replace, merge, delete for
objects and arrays • Merge keys for array elements • Schema defined defaults • Client directive overrides

@jrbowes Strategic Merge Patch ... metadata: labels: service: worker app:
marketplace spec: containers: - image: manifold/worker:1.31.18 name: worker

@jrbowes Strategic Merge Patch spec: containers: - image: manifold/sidecar:1.0.0 name:
metrics

@jrbowes Strategic Merge Patch ... spec: containers: - image: manifold/worker:1.31.18
name: worker - image: manifold/sidecar:1.0.0 name: metrics

@jrbowes Strategic Merge Patch spec: containers: - image: manifold/sidecar:1.0.0 name:
metrics - $patch: replace

@jrbowes lastAppliedConfiguration PROVIDES RICH CONTEXT

@jrbowes PRESERVE THE INTENT OF EVERY CLIENT

@jrbowes @jrbowes Photo by Gamze Bozkaya on Unsplash THE INTERNAL
MODEL

@jrbowes @jrbowes

@jrbowes @jrbowes Photo by David Kovalenko on Unsplash LOST DATA

@jrbowes @jrbowes

@jrbowes @jrbowes Photo by Fabrizio Verrecchia on Unsplash SLOW REACTIONS

@jrbowes @jrbowes

@jrbowes @jrbowes Photo by Matt Artz on Unsplash PREVENTION AND
REPAIR

@jrbowes Lost Intermediate Data • Edge triggered ◦ Track last
seen revision number ◦ Perform a resync on missing version • Not an issue for level triggered

@jrbowes Stale Data • Heartbeat • Periodic resync (done in
Kubernetes)

@jrbowes Slow Reactions • Edge triggered ◦ Keep state for
last value ◦ Compute change to apply with real value, last seen, and changed • Not an issue for level triggered

@jrbowes @jrbowes

@jrbowes KEEP THE CONSUMER LOGIC SIMPLE

@jrbowes @jrbowes Photo by Hans-Peter Gauster on Unsplash PIECING IT
TOGETHER

@jrbowes Controllers are Clients, too • resourceVersion is used for
watching • Controllers may implement their own lastAppliedConfiguration • Different annotations allow unique targeting

@jrbowes TCP implementations should follow a general principle of robustness:
be conservative in what you do, be liberal in what you accept from others. - Jon Postel, RFC 761

@jrbowes be exhaustive in what you send, be explicit in
what you receive from others.

@jrbowes @jrbowes Photo by Annie Spratt on Unsplash WRAPPING UP

@jrbowes @jrbowes Photo by Michael Hoyt on Unsplash COLOCATE COMPLEX
LOGIC WITH STATE

@jrbowes @jrbowes Photo by Roman Koester on Unsplash IDENTIFY THE
AUDIENCE AND BUILD FOR THEM

@jrbowes @jrbowes Photo by Andrés Canchón on Unsplash MAKE IT
HARD FOR THE AUDIENCE TO FAIL

@jrbowes Thank you!

Level Triggered and Reconciled: How Kubernetes Manages its State

Level Triggered and Reconciled: How Kubernetes Manages its State

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