Network Working Group I. Nadareishvili
Internet-Draft October 27, 2018
Intended status: Informational
Expires: April 30, 2019

Health Check Response Format for HTTP APIs
draft-inadarei-api-health-check-03

Abstract

This document proposes a service health check response format for HTTP APIs.

Note to Readers

RFC EDITOR: please remove this section before publication

The issues list for this draft can be found at https://github.com/inadarei/rfc-healthcheck/issues.

The most recent draft is at https://inadarei.github.io/rfc-healthcheck/.

Recent changes are listed at https://github.com/inadarei/rfc-healthcheck/commits/master.

See also the draft’s current status in the IETF datatracker, at https://datatracker.ietf.org/doc/draft-inadarei-api-health-check/.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on April 30, 2019.

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Table of Contents

1. Introduction

The vast majority of modern APIs driving data to web and mobile applications use HTTP [RFC7230] as their protocol. The health and uptime of these APIs determine availability of the applications themselves. In distributed systems built with a number of APIs, understanding the health status of the APIs and making corresponding decisions, for caching, failover or circuit-breaking, are essential to the ability of providing highly-available solutions.

There exists a wide variety of operational software that relies on the ability to read health check response of APIs. However, there is currently no standard for the health check output response, so most applications either rely on the basic level of information included in HTTP status codes [RFC7231] or use task-specific formats.

Usage of task-specific or application-specific formats creates significant challenges, disallowing any meaningful interoperability across different implementations and between different tooling.

Standardizing a format for health checks can provide any of a number of benefits, including:

This document defines a “health check” format using the JSON format [RFC8259] for APIs to use as a standard point for the health information they offer. Having a well-defined format for this purpose promotes good practice and tooling.

2. Notational Conventions

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in [RFC2119].

3. API Health Response

Health Check Response Format for HTTP APIs uses the JSON format described in [RFC8259] and has the media type “application/health+json”.

Its content consists of a single mandatory root field (“status”) and several optional fields:

3.1. status

status: (required) indicates whether the service status is acceptable or not. API publishers SHOULD use following values for the field:

The value of the status field is case-insensitive and is tightly related with the HTTP response code returned by the health endpoint. For “pass” status, HTTP response code in the 2xx-3xx range MUST be used. For “fail” status, HTTP response code in the 4xx-5xx range MUST be used. In case of the “warn” status, endpoints MUST return HTTP status in the 2xx-3xx range, and additional information SHOULD be provided, utilizing optional fields of the response.

A health endpoint is only meaningful in the context of the component it indicates the health of. It has no other meaning or purpose. As such, its health is a conduit to the health of the component. Clients SHOULD assume that the HTTP response code returned by the health endpoint is applicable to the entire component (e.g. a larger API or a microservice). This is compatible with the behavior that current infrastructural tooling expects: load-balancers, service discoveries and others, utilizing health-checks.

3.2. version

version: (optional) public version of the service.

3.3. releaseId

releaseId: (optional) in well-designed APIs, backwards-compatible changes in the service should not update a version number. APIs usually change their version number as infrequently as possible, to preserve stable interface. However implementation of an API may change much more frequently, which leads to the importance of having separate “release number” or “releaseID” that is different from the public version of the API.

3.4. notes

notes: (optional) array of notes relevant to current state of health

3.5. output

output: (optional) raw error output, in case of “fail” or “warn” states. This field SHOULD be omitted for “pass” state.

3.6. details

details (optional) is an object that provides more details about the status of the service as it pertains to the information about the downstream dependencies of the service in question. Please refer to the “The Details Object” section for more information.

3.7. links

links (optional) is an array of objects containing link relations and URIs [RFC3986] for external links that MAY contain more information about the health of the endpoint. Per web-linking standards [RFC8288] a link relationship SHOULD either be a common/registered one or be indicated as a URI, to avoid name clashes. If a “self” link is provided, it MAY be used by clients to check health via HTTP response code, as mentioned above.

3.8. serviceId

serviceId (optional) is a unique identifier of the service, in the application scope.

3.9. description

description (optional) is a human-friendly description of the service.

4. The Details Object

The “details” object MAY have a number of unique keyes, one for each logical downstream dependencies or sub-components. Since each sub-component may be backed by several nodes with varying health statuses, these keys point to arrays of objects. In case of a single-node sub-component (or if presence of nodes is not relevant), a single-element array should be used as the value, for consistency.

The key identifying an element in the object should be a unique string within the details section. It MAY have two parts: “{componentName}:{measurementName}”, in which case the meaning of the parts SHOULD be as follows:

On the value side of the equation, each “component details” object in the array MAY have one of the following object keys:

4.1. componentId

componentId: (optional) is a unique identifier of an instance of a specific sub-component/dependency of a service. Multiple objects with the same componentID MAY appear in the details, if they are from different nodes.

4.2. componentType

componentType: (optional) SHOULD be present if componentName is present. It’s a type of the component and could be one of:

4.3. observedValue

observedValue: (optional) could be any valid JSON value, such as: string, number, object, array or literal.

4.4. observedUnit

observedUnit (optional) SHOULD be present if observedValue is present. Calrifies the unit of measurement in which observedUnit is reported, e.g. for a time-based value it is important to know whether the time is reported in seconds, minutes, hours or something else. To make sure unit is denoted by a well-understood name or an abbreviation, it should be one of:

4.5. status

status (optional) has the exact same meaning as the top-level “output” element, but for the sub-component/downstream dependency represented by the details object.

4.6. time

time (optional) is the date-time, in ISO8601 format, at which the reading of the observedValue was recorded. This assumes that the value can be cached and the reading typically doesn’t happen in real time, for performance and scalability purposes.

4.7. output

output (optional) has the exact same meaning as the top-level “output” element, but for the sub-component/downstream dependency represented by the details object.

4.8. links

links (optional) has the exact same meaning as the top-level “output” element, but for the sub-component/downstream dependency represented by the details object.

5. Example Output

  GET /health HTTP/1.1
  Host: example.org
  Accept: application/health+json

  HTTP/1.1 200 OK
  Content-Type: application/health+json
  Cache-Control: max-age=3600
  Connection: close

{
  "status": "pass",
  "version": "1",
  "releaseID": "1.2.2",
  "notes": [""],
  "output": "",
  "serviceID": "f03e522f-1f44-4062-9b55-9587f91c9c41",
  "description": "health of authz service",
  "details": {
    "cassandra:responseTime": [
      {
        "componentId": "dfd6cf2b-1b6e-4412-a0b8-f6f7797a60d2",
        "componentType": "datastore",
        "observedValue": 250,
        "observedUnit": "ms",
        "status": "pass",
        "time": "2018-01-17T03:36:48Z",
        "output": ""
      }
    ],
    "cassandra:connections": [
      {
        "componentId": "dfd6cf2b-1b6e-4412-a0b8-f6f7797a60d2",
        "type": "datastore",
        "observedValue": 75,
        "status": "warn",
        "time": "2018-01-17T03:36:48Z",
        "output": "",
        "links": {
          "self": "http://api.example.com/dbnode/dfd6cf2b/health"
        }
      }
    ],
    "uptime": [
      {
        "componentType": "system",
        "observedValue": 1209600.245,
        "observedUnit": "s",
        "status": "pass",
        "time": "2018-01-17T03:36:48Z"
      }
    ],
    "cpu:utilization": [
      {
        "componentId": "6fd416e0-8920-410f-9c7b-c479000f7227",
        "node": 1,
        "componentType": "system",
        "observedValue": 85,
        "observedUnit": "percent",
        "status": "warn",
        "time": "2018-01-17T03:36:48Z",
        "output": ""
      },
      {
        "componentId": "6fd416e0-8920-410f-9c7b-c479000f7227",
        "node": 2,
        "componentType": "system",
        "observedValue": 85,
        "observedUnit": "percent",
        "status": "warn",
        "time": "2018-01-17T03:36:48Z",
        "output": ""
      }
    ],
    "memory:utilization": [
      {
        "componentId": "6fd416e0-8920-410f-9c7b-c479000f7227",
        "node": 1,
        "componentType": "system",
        "observedValue": 8.5,
        "observedUnit": "GiB",
        "status": "warn",
        "time": "2018-01-17T03:36:48Z",
        "output": ""
      },
      {
        "componentId": "6fd416e0-8920-410f-9c7b-c479000f7227",
        "node": 2,
        "componentType": "system",
        "observedValue": 5500,
        "observedUnit": "MiB",
        "status": "pass",
        "time": "2018-01-17T03:36:48Z",
        "output": ""
      }
    ]
  },
  "links": {
    "about": "http://api.example.com/about/authz",
    "http://api.x.io/rel/thresholds":
      "http://api.x.io/about/authz/thresholds"
  }
}

6. Security Considerations

Clients need to exercise care when reporting health information. Malicious actors could use this information for orchestrating attacks. In some cases the health check endpoints may need to be authenticated and institute role-based access control.

7. IANA Considerations

The media type for health check response is application/health+json.

8. Acknowledgements

Thanks to Mike Amundsen, Erik Wilde, Justin Bachorik and Randall Randall for their suggestions and feedback. And to Mark Nottingham for blueprint for authoring RFCs easily.

9. Creating and Serving Health Responses

When making an health check endpoint available, there are a few things to keep in mind:

10. Consuming Health Check Responses

Clients might use health check responses in a variety of ways.

Note that the health check response is a “living” document; links from the health check response MUST NOT be assumed to be valid beyond the freshness lifetime of the health check response, as per HTTP’s caching model [RFC7234].

As a result, clients ought to cache the health check response (as per [RFC7234]), to avoid fetching it before every interaction (which would otherwise be required).

Likewise, a client encountering a 404 (Not Found) on a link is encouraged to obtain a fresh copy of the health check response, to assure that it is up-to-date.

11. References

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005.
[RFC7234] Fielding, R., Nottingham, M. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, DOI 10.17487/RFC7234, June 2014.
[RFC8259] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", STD 90, RFC 8259, DOI 10.17487/RFC8259, December 2017.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017.

11.2. Informative References

[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002.
[RFC6838] Freed, N., Klensin, J. and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, January 2013.
[RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014.
[RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014.

Author's Address

Irakli Nadareishvili 114 5th Avenue New York, United States EMail: irakli@gmail.com URI: http://www.freshblurbs.com