Network Working Group I. Nadareishvili
Internet-Draft 18 November 2020
Intended status: Informational
Expires: 22 May 2021
Health Check Response Format for HTTP APIs
draft-inadarei-api-health-check-05
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
(https://github.com/inadarei/rfc-healthcheck/issues).
The most recent draft is at https://inadarei.github.io/rfc-
healthcheck/ (https://inadarei.github.io/rfc-healthcheck/).
Recent changes are listed at https://github.com/inadarei/rfc-
healthcheck/commits/master (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/
(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.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 22 May 2021.
Copyright Notice
Copyright (c) 2020 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
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3
3. API Health Response . . . . . . . . . . . . . . . . . . . . . 4
3.1. status . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. version . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.3. releaseId . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. notes . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5. output . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.6. checks . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.7. links . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.8. serviceId . . . . . . . . . . . . . . . . . . . . . . . . 5
3.9. description . . . . . . . . . . . . . . . . . . . . . . . 5
4. The Checks Object . . . . . . . . . . . . . . . . . . . . . . 6
4.1. componentId . . . . . . . . . . . . . . . . . . . . . . . 7
4.2. componentType . . . . . . . . . . . . . . . . . . . . . . 7
4.3. observedValue . . . . . . . . . . . . . . . . . . . . . . 7
4.4. observedUnit . . . . . . . . . . . . . . . . . . . . . . 7
4.5. status . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.6. affectedEndpoints . . . . . . . . . . . . . . . . . . . . 8
4.7. time . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.8. output . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.9. links . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.10. Additional Keys . . . . . . . . . . . . . . . . . . . . . 9
5. Example Output . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. Creating and Serving Health Responses . . . . . . . . . . . . 13
10. Consuming Health Check Responses . . . . . . . . . . . . . . 13
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
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11.1. Normative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
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:
* Flexible deployment - since operational tooling and API clients
can rely on rich, uniform format, they can be safely combined and
substituted as needed.
* Evolvability - new APIs, conforming to the standard, can safely be
introduced in any environment and ecosystem that also conforms to
the same standard, without costly coordination and testing
requirements.
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].
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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:
* "pass": healthy (acceptable aliases: "ok" to support Node's
Terminus and "up" for Java's SpringBoot),
* "fail": unhealthy (acceptable aliases: "error" to support Node's
Terminus and "down" for Java's SpringBoot), and
* "warn": healthy, with some concerns.
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.
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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. checks
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.
3.7. links
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.
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.
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4. The Checks Object
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:
* componentName: (optional) human-readable name for the component.
MUST not contain a colon, in the name, since colon is used as a
separator.
* measurementName: (optional) name of the measurement type (a data
point type) that the status is reported for. MUST not contain a
colon, in the name, since colon is used as a separator. The
observation's name can be one of:
- A pre-defined value from this spec. Pre-defined values
include:
o utilization
o responseTime
o connections
o uptime
- A common and standard term from a well-known source such as
schema.org, IANA or microformats.
- A URI that indicates extra semantics and processing rules that
MAY be provided by a resource at the other end of the URI.
URIs do not have to be dereferenceable, however. They are just
a namespace, and the meaning of a namespace CAN be provided by
any convenient means (e.g. publishing an RFC, Open API Spec
document or a nicely printed book).
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:
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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:
* Pre-defined value from this spec. Pre-defined values include:
- component
- datastore
- system
* A common and standard term from a well-known source such as
schema.org, IANA or microformats.
* A URI that indicates extra semantics and processing rules that MAY
be provided by a resource at the other end of the URI. URIs do
not have to be dereferenceable, however. They are just a
namespace, and the meaning of a namespace CAN be provided by any
convenient means (e.g. publishing an RFC, Swagger document or a
nicely printed book).
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. 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:
* A common and standard term from a well-known source such as
schema.org, IANA, microformats, or a standards document such as
[RFC3339].
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* A URI that indicates extra semantics and processing rules that MAY
be provided by a resource at the other end of the URI. URIs do
not have to be dereferenceable, however. They are just a
namespace, and the meaning of a namespace CAN be provided by any
convenient means (e.g. publishing an RFC, Swagger document or a
nicely printed book).
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. affectedEndpoints
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.
4.7. 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.
4.8. 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. As is the case for the top-level
element, this field SHOULD be omitted for "pass" state of a
downstream dependency.
4.9. 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.
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4.10. Additional Keys
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.
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",
"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",
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"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": ""
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},
{
"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.
* Media type name: application
* Media subtype name: health+json
* Required parameters: n/a
* Optional parameters: n/a
* Encoding considerations: binary
* Security considerations: Health+JSON shares security issues common
to all JSON content types. See RFC 8259 Section #12 for
additional information.
Health+JSON allows utilization of Uniform Resource Identifiers
(URIs) and as such shares security issues common to URI usage.
See RFC 3986 Section #7 for additional information.
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Since health+json can carry wide variety of data, some data may
require privacy or integrity services. This specification does
not prescribe any specific solution and assumes that concrete
implementations will utilize common, trusted approaches such as
TLS/HTTPS, OAuth2 etc.
* Interoperability considerations: None
* Published specification: this RFC draft
* Applications which use this media: Various
* Fragment identifier considerations: Health+JSON follows RFC6901
for implementing URI Fragment Identification standard to JSON
content types.
* Restrictions on usage: None
* Additional information:
1. Deprecated alias names for this type: n/a
2. Magic number(s): n/a
3. File extension(s): .json
4. Macintosh file type code: TEXT
5. Object Identifiers: n/a
* General Comments:
* Person to contact for further information:
1. Name: Irakli Nadareishvili
2. Email: irakli@gmail.com
* Intended usage: Common
* Author/Change controller: Irakli Nadareishvili
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.
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9. Creating and Serving Health Responses
When making an health check endpoint available, there are a few
things to keep in mind:
* A health response endpoint is best located at a memorable and
commonly-used URI, such as "health" because it will help self-
discoverability by clients.
* Health check responses can be personalized. For example, you
could advertise different URIs, and/or different kinds of link
relations, to afford different clients access to additional health
check information.
* Health check responses SHOULD be assigned a freshness lifetime
(e.g., "Cache-Control: max-age=3600") so that clients can
determine how long they could cache them, to avoid overly frequent
fetching and unintended DDOS-ing of the service. Any method of
cache lifetime negotiation provided by HTTP spec is acceptable
(e.g. ETags are just fine).
* Custom link relation types, as well as the URIs for variables,
SHOULD lead to documentation for those constructs.
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
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/info/rfc6570>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<https://www.rfc-editor.org/info/rfc7234>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
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,
<https://www.rfc-editor.org/info/rfc3339>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
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[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
Author's Address
Irakli Nadareishvili
114 5th Avenue
New York,
United States of America
Email: irakli@gmail.com
URI: http://www.freshblurbs.com
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