| Network Working Group | I. Nadareishvili |
| Internet-Draft | December 31, 2019 |
| Intended status: Informational | |
| Expires: July 3, 2020 |
Health Check Response Format for HTTP APIs
draft-inadarei-api-health-check-04
This document proposes a service health check response format for HTTP APIs.
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/.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 3, 2020.
Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
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.
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].
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:
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.
version: (optional) public version of the service.
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.
notes: (optional) array of notes relevant to current state of health
output: (optional) raw error output, in case of “fail” or “warn” states. This field SHOULD be omitted for “pass” state.
checks (optional) is an object that provides detailed health statuses of additional downstream systems and endpoints which can affect the overall health of the main API. Please refer to the “The Checks Object” section for more information.
links (optional) is an object containing link relations and URIs [RFC3986] for external links that MAY contain more information about the health of the endpoint. All values of this object SHALL be URIs. Keys MAY also be URIs. 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.
serviceId (optional) is a unique identifier of the service, in the application scope.
description (optional) is a human-friendly description of the service.
The “checks” object MAY have a number of unique keys, one for each logical downstream dependency or sub-component. 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 SHOULD have at least one key, and MAY have any or none of the following object keys:
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.
componentType: (optional) SHOULD be present if componentName is present. It’s a type of the component and could be one of:
observedValue: (optional) could be any valid JSON value, such as: string, number, object, array or literal.
observedUnit (optional) SHOULD be present if observedValue is present. Clarifies 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:
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.
affectedEndpoints (optional) is a JSON array containing URI Templates as defined by [RFC6570]. This field SHOULD be omitted if the “status” field is present and has value equal to “pass”. A typical API has many URI endpoints. Most of the time we are interested in the overall health of the API, without diving into details. That said, sometimes operational and resilience middleware needs to know more details about the health of the API (which is why “checks” property provides details). In such cases, we often need to indicate which particular endpoints are affected by a particular check’s troubles vs. other endpoints that may be fine.
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.
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. As is the case for the top-level element, this field SHOULD be omitted for “pass” state of a downstream dependency.
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.
In addition to the above keys, additional user-defined keys MAY be included in the ‘component details’ object. Implementations MAY ignore any keys that are not part of the list of standard keys above.
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",
"checks": {
"cassandra:responseTime": [
{
"componentId": "dfd6cf2b-1b6e-4412-a0b8-f6f7797a60d2",
"componentType": "datastore",
"observedValue": 250,
"observedUnit": "ms",
"status": "pass",
"affectedEndpoints" : [
"/users/{userId}",
"/customers/{customerId}/status",
"/shopping/{anything}"
],
"time": "2018-01-17T03:36:48Z",
"output": ""
}
],
"cassandra:connections": [
{
"componentId": "dfd6cf2b-1b6e-4412-a0b8-f6f7797a60d2",
"componentType": "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"
}
}
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.
The media type for health check response is application/health+json.
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.
When making an health check endpoint available, there are a few things to keep in mind:
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.
| [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. |
| [RFC6570] | Gregorio, J., Fielding, R., Hadley, M., Nottingham, M. and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012. |
| [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. |
| [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. |