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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
   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."




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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
   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.

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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Internet-Draft  Health Check Response Format for HTTP AP   November 2020


   [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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