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Istio API Guidelines

This page defines the design guidelines for Istio APIs. They apply to Kubernetes Custom Resource Definitions and all proto files that are used to configure Istio components through the Mesh Configuration Protocol(MCP).

Since MCP is based on proto3 and gRPC, we will use Google's API Design Guide as the baseline for protos. Because Envoy APIs also uses the same baseline, the commonality across Envoy, Istio, proto3 and gRPC will greatly help developer experience in the long term.

In addition to Google's guide, the following conventions should be followed for Istio APIs.

Contents

Proto Guidelines

This section captures guidelines that apply to the proto form of the configuration resources.

Style

Placement

  • Do place new API protos under istio.io/api/<area>/<version> folder.
  • Prefer complete words for file names.
    • config.proto // Not cfg.proto!

Package Names

  • Do use lowercase without any _.
  • Do use singular words
  • Do use the name pattern istio.<area>.<version>.
package istio.networking.v1alpha3;

Message/Enum/Method Names

  • Do not use embedded acronyms. See #364 for details.
message HttpRequest {/*...*/}  // Not HTTPRequest!

rpc DoHttpRequest(/*...*/)     // Not DoHTTPRequest!

enum HttpStatusCodes {/*...*/} // Not HTTPStatusCodes!

Messages

  • Do use CamelCase for message names. 
    • message MyMessage {...}

Fields

  • Do use lowercase_with_underscore for field names: 
    • string display_name = 1;
  • Do use plural names for repeated fields: 
    • repeated rule rules = 2;
  • Do not use postpositive adjectives in names. 
    • repeated Items collected_items = 3; // Not items_collected!

Enums

  • Do use CamelCase for types names. 
    • enum Types {/*...*/}
  • Do use UPPERCASE_WITH_UNDERSCORE for enum names: 
    • enum Types {INT_TYPE = 1;}
  • Do have an enum entry for value 0.
    • When a new field with an enum type is introduced to a proto, when reading the older versions of the data, it will be defaulted to 0 value.
  • Do name the 0 value either as <ENUMTYPE>_UNDEFINED or use a sane, well-known value that will be considered as default. 
    • enum Types { TYPE_UNDEFINED = 0;}

Basic Proto Versioning

Protocol Buffers have well-defined semantics for coping with version changes. In essense, the unknown fields get ignored, and additive, and non-breaking changes are acceptable.

In addition to the standard proto versioning semantics, Istio tooling imposes its own restrictions, as CRD to proto conversion system in Istio depends on names in certain situations.

The following rules captures the basic rules that should be followed when making changes to Istio config protos.

  • Do not change field numbers.
    • Proto depends on field numbers to find fields.
    •     // Field number has changed from 1 to 2!
    
    // string field = 1; // Deleted
    string field = 2;
  • Do not rename fields.
    • Our tooling automatically maps YAML fields to proto fields.
    •     // Field name has changed!
    
    // string old_field = 1;
    string new_field = 1;
  • Do not change cardinality of fields. 
    •     // Field cardinality has changed!
    
    // string should_have_been_plural = 1;
    repeated string should_have_been_plural = 1;
  • Do not rename top-level protos that map to CRD config types.
    • Istio tooling depends on the name of the top-level protos to map CRDs to the matching proto counterparts.
       // Top-level proto name has changed!
 
   // message Rule {
   message PolicyRule {
        // ...
   }
  • Avoid changing/renaming field types.
    • If the field types changes, the new type must be structurally equivalent to the old.
        // Field type changed from Boo to Zoo!
    // Boo and Zoo must be structurally equivalent!
    message Foo {
       // Boo boo = 1;  
       Zoo boo = 2;
    }
  • Do not rename enum names, or change values.
    • Istio tooling depends on names to convert enums from CRD form to proto.
    •     enum Types {
       // Enum name has changed!
       // Foo = 1;
       Bar = 1;

       // Enum value has changed!
       // Baz = 2;
       Baz = 3;

    }

CRD Guidelines

Style

  • Do use the name pattern <area>.istio.io for API group names.
  • Do use the version from the proto package as the API version.
  • Do use the top-level proto Message name as the kind of the CRD.
# A custom resource that describes a Gateway resource
apiVersion: networking.istio.io/v1alpha3
kind: Gateway 
# ...

Matches to:

package istio.networking.v1alpha3;
message Gateway {
    // ...
}

Basic CRD Versioning

Istio APIs should use a simple versioning strategy based on major versions and releases, such as v1alpha, v2beta, or v3. Within each release, there should not be any breaking change to released features, such as changing the type of a field type, renaming a field, or changing a field number. Breaking changes are allowed between different releases, such as v1alpha1 and v1alpha2.

Deprecating a feature in an API release is allowed by following the applicable deprecation process. The reason to allow deprecation of individual features in a release is that it is significantly cheaper and simpler for everyone involved. In practice, it works out much better than deprecating an entire API version.