Moving "routing mode" to the route (from service)

[cppforlife]

/area API
/kind feature

Currently Service object has two fields runLatest and pinned [1]. They control how service manages associated Route object:

• runLatest: service will make sure route points to the latest ready revision
• pinned: service will make sure route points to a particular revision

As a side effect, if a user is using Service object to manage Configuration and Route objects, there is no way to do traffic splitting, because if route is reconfigured, service controller will just reconcile it based on two above configurations. (To do traffic splitting, user would actually have to stop using service object and managed configuration and route objects directly.)

Proposed change:

type Service struct {
	Spec ServiceSpec
}

type ServiceSpec struct {
	Configuration ConfigurationSpec
}

^ removes runLatest and pinned types from Service.Spec

// part of Route spec

type TrafficTarget struct {
	Name string
	RevisionName string
	ConfigurationName string
	Percent int
}

^ TrafficTarget (and Route) does not change, as it already supports running latest ready revision of particular Configuration object (via ConfigurationName) or pointing to particular revision (via RevisionName) (pins traffic to particular revision).

Few cases:

• user wants service to point to latest ready revision (everything stays as is since it's the default route configuration created by the service); as new revisions are made route automatically picks up new ready revision
• user wants configure service to route traffic to two revisions; user would create a service, then configure route to point to two revisions with appropriate weights, service controller will not reconfigure it

Benefits:

• moves towards use of Service object, instead of having two ways (via Service and with Configuration+Route)
• removes somewhat confusing fields from Service (runLatest and pinned) and some ambiguity
• can do traffic splitting with a Service object
• abides by routing configuration on the Route object

---

[1]

serving/pkg/apis/serving/v1alpha1/service_types.go

Lines 72 to 81 in b1d14bd

	// RunLatest defines a simple Service. It will automatically
	// configure a route that keeps the latest ready revision
	// from the supplied configuration running.
	// +optional
	RunLatest *RunLatestType `json:"runLatest,omitempty"`
	// Pins this service to a specific revision name. The revision must
	// be owned by the configuration provided.
	// +optional
	Pinned *PinnedType `json:"pinned,omitempty"`

[mattmoor]

Since there's no way to control the Route spec via Service, this effectively eliminates the ability to express "pinned".

[mattmoor]

cc @mikehelmick @cooperneil

[mattmoor]

This is similar to a sentiment I expressed on one of the earlier proposals for "Steve" (what's now "Service"), which is that some of the rollout options were probably most relevant on TrafficTarget with a ConfigurationName to control how LatestReadyRevisionName is rolled out.

[cppforlife]

@mattmoor

Since there's no way to control the Route spec via Service, this effectively eliminates the ability to express "pinned".

i imagine user will just simply update route object to use particular RevisionName for pinning. not a big difference between configuring service object imho.

[sixolet]

The purpose of Service is to act as a clearinghouse for rollout/rollback policies; if the user wants to control these in a fine-grained way using Route, there's no reason for that user to use Service at all.

Service is likely to grow more options than runLatest and pinned, and become more useful in that way.

[mattmoor]

To clarify, I don't think that these are mutually exclusive either. We may want to build the extra sophistication at the "Steve" level via a rollout option, that exposes richer functionality that's implemented at the TrafficTarget level. However, I'm not sure this will always be the case.

[cppforlife]

related: #1870

[voor]

Isn't the intention that if you were to push a new revision using the same containers, you would then have the option to rollback to an earlier traffic split pattern if something were to go wrong? So instead of editing a route to change traffic to 50/50, you should push a new revision with a 50/50 split, and if something were to go wrong you would then have the option to rollback to an earlier traffic pattern?

[steren]

@sixolet said:

The purpose of Service is to act as a clearinghouse for rollout/rollback policies; if the user wants to control these in a fine-grained way using Route, there's no reason for that user to use Service at all.

This is not correct. When we introduced the Service object, the intent was not to prevent users from controlling the Route. It was introduced to solve the problems stated in #412.

And as @mikehelmick commented in #412 (comment), the agreement was to provide a "manual mode". I am not sure why this was not implemented.

we will also specify a new manual mode where the user is free to interact with the resources created by the service object directly

[mikehelmick]

Hello. Here I have a solution to the issues raised here.
I want to start by referring back to the original Service proposal, #412 (comment)

In this, we discussed a future manual mode for service that allows the user to manipulate their associated Route and Configuration objects directly, without the Service controller continuing to reconcile those objects.

Objective

The Service object ("Steve") originally implemented two modes, RunLatest and Pinned. These modes allow a user to always have the latest Revision running at 100% of traffic or to pin a specific revision to 100% of traffic.

Here, we formally propose a new mode for controlled releases (called simply “Release” mode, that also replaces the functionality of pinned mode. (Pinned mode will be marked as deprecated)

The opinionated release process here, provides a way for a user to automatically promote new releases, gradually roll out new releases, and rollback to a known good release.

We also formally introduce the long rumored “manual mode” that allows for full control over the route object.

This closes out the modes of Service that will be created unless user feedback tells us that other scenarios are needed.

Deprecation of Pinned Mode

Pinned mode of service exists in v1alpha1. We propose to drop pinned mode from future releases, and replace it with release mode (below) that provides the same functionality and extends it further.

The existing functionality of Pinned mode can be enacted by using release mode and setting the revision list to size of 1.

Introduction of Release Mode

The principle of release mode is that it provides an easy way for a user to gradually promote a new release, and also contains the existing functionality of pinned mode. Release mode gives an opinionated way of performing release management, giving well-known subroute names (current, next, and latest).

The specification for release mode is:

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
  name: Counter 
spec:
  Release:
    # An ordered list of 1 or 2 revisions. The first have a TrafficTarget
    # with a name of "current" and the second will have a name of "next"
    revisions: ["Counter.1", "Counter.4"]
    # Percent of traffic that should be sent to the next revision. Valid values
    # are between 0 and 99 inclusive. 
    rolloutPercent: 50   
    # All revisions referenced must come from this configuration.
    # The latest revision from head, will be available at a 0 percent TrafficTarget
    # with a name of 'latest'
    configuration:
      ...
status:
  ... 
  # The TrafficTarget array will reflect the effective traffic splits

This provides a simple, intuitive way for users to have a disciplined release process, gradually moving from one release to another.

It provides standardized naming for current, next, and latest and an easy way to manage your release process.

Manual Mode

RunLatest and Release modes cover common user scenarios. If a user starts in Service mode, but later needs more advanced functionality, they need to be able to directly access the route and configuration objects, but may still want to enforce grouping under the Service.

When in manual mode, the service controller does not attempt to reconcile the configuration or the route.

manual mode simply references the ``Route and Configuration by name. The implementation of the Knative API may prevent a service from being created in manual mode, requiring it to be created in RunLatest or Release and then transitioned to manual.

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
  name: Counter
spec: 
  # The user is in complete control of the route and configuration that
  #  are part of this service. The service controller will not attempt
  #  reconcile changes.
  manual: {}
status:
  ...

Implementation Considerations

The proposed changes here are fully in the spirit of Knative Service object, providing an “easy mode” for developers to manage their service. It also provides an exit to manual mode if more powerful functionality is desired.