ETSI GS MEC 009 V2.1.1 (2019-01)

Multi-access Edge Computing (MEC); General principles for MEC Service APIs

RGS/MEC-0009v211ApiPrinciples

General Information

• Status: Published
• Publication Date: 21-Jan-2019
• Technical Committee: MEC - Multi-access Edge Computing
• Current Stage: 12 - Completion
• Due Date: 31-Jan-2019
• Completion Date: 22-Jan-2019

Standards Content (Sample)

GROUP SPECIFICATION
Multi-access Edge Computing (MEC);
General principles for MEC Service APIs
Disclaimer
The present document has been produced and approved by the Multi-access Edge Computing (MEC) ETSI Industry
Specification Group (ISG) and represents the views of those members who participated in this ISG.
It does not necessarily represent the views of the entire ETSI membership.

2 ETSI GS MEC 009 V2.1.1 (2019-01)

Reference
RGS/MEC-0009v211ApiPrinciples
Keywords
API, MEC
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3 ETSI GS MEC 009 V2.1.1 (2019-01)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
1 Scope . 7
2 References . 7
2.1 Normative references . 7
2.2 Informative references . 8
3 Definition of terms, symbols and abbreviations . 9
3.1 Terms . 9
3.2 Symbols . 9
3.3 Abbreviations . 10
4 Design principles for developing RESTful MEC service APIs . 10
4.1 REST implementation levels . 10
4.2 General principles. 10
4.3 Entry point of a RESTful MEC service API . 11
4.4 API security and privacy considerations . 11
5 Documenting RESTful MEC service APIs . 11
5.1 RESTful MEC service API template . 11
5.2 Conventions for names . 12
5.2.1 Case conventions . 12
5.2.2 Conventions for URI parts . 12
5.2.2.1 Introduction . 12
5.2.2.2 Path segment naming conventions . 13
5.2.2.3 Query naming conventions . 13
5.2.3 Conventions for names in data structures . 13
5.3 Provision of an OpenAPI definition . 14
6 Patterns of RESTful MEC service APIs . 14
6.1 Introduction . 14
6.2 void . 14
6.3 Pattern: Resource identification . 14
6.3.1 Description . 14
6.3.2 Resource definition(s) and HTTP methods . 14
6.4 Pattern: Resource representations and content format negotiation . 15
6.4.1 Description . 15
6.4.2 Resource definition(s) and HTTP methods . 15
6.4.3 Resource representation(s) . 15
6.4.4 HTTP headers . 15
6.4.5 Response codes and error handling . 16
6.5 Pattern: Creating a resource (POST) . 16
6.5.1 Description . 16
6.5.2 Resource definition(s) and HTTP methods . 16
6.5.3 Resource representation(s) . 17
6.5.4 HTTP headers . 17
6.5.5 Response codes and error handling . 17
6.5a Pattern: Creating a resource (PUT) . 17
6.5a.1 Description . 17
6.5a.2 Resource definition(s) and HTTP methods . 18
6.5a.3 Resource representation(s) . 18
6.5a.4 HTTP headers . 18
6.5a.5 Response codes and error handling . 18
6.6 Pattern: Reading a resource . 18
6.6.1 Description . 18
6.6.2 Resource definition(s) and HTTP methods . 19
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6.6.3 Resource representation(s) . 19
6.6.4 HTTP headers . 19
6.6.5 Response codes and error handling . 19
6.7 Pattern: Queries on a resource . 19
6.7.1 Description . 19
6.7.2 Resource definition(s) and HTTP methods . 20
6.7.3 Resource representation(s) . 20
6.7.4 HTTP headers . 20
6.7.5 Response codes and error handling . 20
6.8 Pattern: Updating a resource (PUT) . 20
6.8.1 Description . 20
6.8.2 Resource definition(s) and HTTP methods . 21
6.8.3 Resource representation(s) . 21
6.8.4 HTTP headers . 21
6.8.5 Response codes and error handling . 22
6.9 Pattern: Updating a resource (PATCH) . 22
6.9.1 Description . 22
6.9.2 Resource definition(s) and HTTP methods . 23
6.9.3 Resource representation(s) . 23
6.9.4 HTTP headers . 24
6.9.5 Response codes and error handling . 24
6.10 Pattern: Deleting a resource. 24
6.10.1 Description . 24
6.10.2 Resource definition(s) and HTTP methods . 25
6.10.3 Resource representation(s) . 25
6.10.4 HTTP headers . 25
6.10.5 Response codes and error handling . 25
6.11 Pattern: Task resources . 26
6.11.1 Description . 26
6.11.2 Resource definition(s) and HTTP methods . 26
6.11.3 Resource representation(s) . 26
6.11.4 HTTP headers . 26
6.11.5 Response codes and error handling . 26
6.12 Pattern: REST-based subscribe/notify . 27
6.12.1 Description . 27
6.12.2 Resource definition(s) and HTTP methods . 28
6.12.3 Resource representation(s) . 29
6.12.4 HTTP headers . 29
6.12.5 Response codes and error handling . 29
6.13 Pattern: Asynchronous operations . 29
6.13.1 Description . 29
6.13.2 Resource definition(s) and HTTP methods . 31
6.13.3 Resource representation(s) . 31
6.13.4 HTTP headers . 32
6.13.5 Response codes and error handling . 32
6.14 Pattern: Links (HATEOAS) . 32
6.14.1 Description . 32
6.14.2 Resource definition(s) and HTTP methods . 32
6.14.3 Resource representation(s) . 32
6.14.4 HTTP headers . 34
6.14.5 Response codes and error handling . 34
6.15 Pattern: Error responses . 34
6.15.1 Description . 34
6.15.2 Resource definition(s) and HTTP methods . 34
6.15.3 Resource representation(s) . 34
6.15.4 HTTP headers . 35
6.15.5 Response codes and error handling . 35
6.16 Pattern: Authorization of access to a RESTful MEC service API using OAuth 2.0 . 35
6.16.1 Description . 35
6.16.2 Resource definition(s) and HTTP methods . 38
6.16.3 Resource representation(s) . 39
6.16.4 HTTP headers . 39
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6.16.5 Response codes and error handling . 39
6.16.6 Discovery of the parameters needed for exchanges with the token endpoint . 39
6.16.7 Scope values . 39
6.17 Pattern: Representation of lists in JSON . 39
6.17.1 Description . 39
6.17.2 Representation as arrays . 39
6.17.3 Representation as maps . 40
6.18 Pattern: Attribute selectors . 40
6.18.1 Description . 40
6.18.2 Resource definition(s) and HTTP methods . 40
6.18.3 Resource representation(s) . 41
6.18.4 HTTP headers . 42
6.18.5 Response codes and error handling . 42
6.19 Pattern: Attribute-based filtering . 42
6.19.1 Description . 42
6.19.2 Resource definition(s) and HTTP methods . 43
6.19.3 Resource representation(s) . 44
6.19.4 HTTP headers . 44
6.19.5 Response codes and error handling . 45
7 Alternative transport mechanisms . 45
7.1 Description . 45
7.2 Relationship of topics, subscriptions and access rights . 46
7.3 Serializers . 47
7.4 Authorization of access to a service over alternative transports using TLS credentials . 48
Annex A (informative): REST methods. 51
Annex B (normative): HTTP response status codes . 52
Annex C (informative): Richardson maturity model of REST APIs . 54
Annex D (informative): RESTful MEC service API template. 55
History . 64

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Intellectual Property Rights
Essential patents
IPRs essential or potentially essential to normative deliverables may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (https://ipr.etsi.org/).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Trademarks
The present document may include trademarks and/or tradenames which are asserted and/or registered by their owners.
ETSI claims no ownership of these except for any which are indicated as being the property of ETSI, and conveys no
right to use or reproduce any trademark and/or tradename. Mention of those trademarks in the present document does
not constitute an endorsement by ETSI of products, services or organizations associated with those trademarks.
Foreword
This Group Specification (GS) has been produced by ETSI Industry Specification Group (ISG) Multi-access Edge
Computing (MEC).
Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.

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1 Scope
The present document defines design principles for RESTful MEC service APIs, provides guidelines and templates for
the documentation of these, and defines patterns of how MEC service APIs use RESTful principles.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
https://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] IETF RFC 7231: "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content".
NOTE: Available at https://tools.ietf.org/html/rfc7231.
[2] IETF RFC 7232: "Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests".
NOTE: Available at https://tools.ietf.org/html/rfc7232.
[3] IETF RFC 5789: "PATCH Method for HTTP".
NOTE: Available at https://tools.ietf.org/html/rfc5789.
[4] IETF RFC 6901: "JavaScript Object Notation (JSON) Pointer".
NOTE: Available at https://tools.ietf.org/html/rfc6901.
[5] IETF RFC 7396: "JSON Merge Patch".
NOTE: Available at https://tools.ietf.org/html/rfc7396.
[6] IETF RFC 6902: "JavaScript Object Notation (JSON) Patch".
NOTE: Available at https://tools.ietf.org/html/rfc6902.
[7] IETF RFC 5261: "An Extensible Markup Language (XML) Patch Operations Framework Utilizing
XML Path Language (XPath) Selectors".
NOTE: Available at https://tools.ietf.org/html/rfc5261.
[8] IETF RFC 6585: "Additional HTTP Status Codes".
NOTE: Available at https://tools.ietf.org/html/rfc6585.
[9] IETF RFC 3986: "Uniform Resource Identifier (URI): Generic Syntax".
NOTE: Available at https://tools.ietf.org/html/rfc63986.
[10] IETF RFC 8259: "The JavaScript Object Notation (JSON) Data Interchange Format".
NOTE: Available at https://tools.ietf.org/html/rfc8259.
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[11] W3C Recommendation 16 August 2006: "Extensible Markup Language (XML) 1.1" (Second
Edition).
NOTE: Available at https://www.w3.org/TR/2006/REC-xml11-20060816/.
[12] IETF RFC 5988: "Web Linking".
NOTE: Available at https://tools.ietf.org/html/rfc5988.
[13] IETF RFC 2818: "HTTP Over TLS".
NOTE: Available at https://tools.ietf.org/html/rfc2818.
[14] IETF RFC 5246: "The Transport Layer Security (TLS) Protocol Version 1.2".
NOTE: Available at https://tools.ietf.org/html/rfc5246.
[15] IETF RFC 7807: "Problem Details for HTTP APIs".
NOTE: Available at https://tools.ietf.org/html/rfc7807.
[16] IETF RFC 6749: "The OAuth 2.0 Authorization Framework".
NOTE: Available at https://tools.ietf.org/html/rfc6749.
[17] IETF RFC 6750: "The OAuth 2.0 Authorization Framework: Bearer Token Usage".
NOTE: Available at https://tools.ietf.org/html/rfc6750.
[18] IETF RFC 7540: "Hypertext Transfer Protocol Version 2 (HTTP/2)".
NOTE: Available at https://tools.ietf.org/html/rfc7540.
[19] IETF RFC 7301: "Transport Layer Security (TLS): Application-Layer Protocol Negotiation
Extension".
NOTE: Available at https://tools.ietf.org/html/rfc7301.
[20] IETF RFC 3339: "Date and Time on the Internet: Timestamps".
NOTE: Available at https://tools.ietf.org/html/rfc3339.
[21] IETF RFC 4918: "HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)".
NOTE: Available at https://tools.ietf.org/html/rfc4918.
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication, ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI GS MEC 001: "Multi-access Edge Computing (MEC); Terminology".
[i.2] William Durand: "Please. Don't Patch Like An Idiot".
NOTE: Available at http://williamdurand.fr/2014/02/14/please-do-not-patch-like-an-idiot/.
[i.3] Martin Fowler: "Richardson Maturity Model: steps toward the glory of REST".
NOTE: Available at http://martinfowler.com/articles/richardsonMaturityModel.html.
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[i.4] JSON Schema, Draft Specification v7, November 19, 2017.
NOTE: Available at http://json-schema.org/specification.html. Also available as Internet Draft (work in progress)
from https://tools.ietf.org/html/draft-handrews-json-schema-00.
[i.5] W3C Recommendation: "XML Schema Part 0: Primer Second Edition".
NOTE: Available at https://www.w3.org/TR/xmlschema-0/.
[i.6] ETSI GS MEC 011: "Multi-access Edge Computing (MEC); Edge Platform Application
Enablement".
[i.7] ETSI GS MEC 012: "Multi-access Edge Computing (MEC); Radio Network Information API".
[i.8] IANA: "Hypertext Transfer Protocol (HTTP) Status Code Registry".
NOTE: Available at http://www.iana.org/assignments/http-status-codes.
[i.9] MQTT Version 3.1.1 Plus Errata 01, OASIS™ Standard, 10 December 2015.
NOTE: Available at http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/mqtt-v3.1.1.html.
[i.10] Apache™ Kafka.
NOTE: Available at https://kafka.apache.org/.
[i.11] GRPC™.
NOTE: Available at http://www.grpc.io/.
[i.12] Protocol buffers.
NOTE: Available at https://developers.google.com/protocol-buffers/.
[i.13] IETF RFC 7519: "JSON Web Token (JWT)".
NOTE: Available at https://tools.ietf.org/html/rfc7519.
[i.14] OpenAPI Specification.
NOTE: Available at https://github.com/OAI/OpenAPI-Specification.
3 Definition of terms, symbols and abbreviations
3.1 Terms
For the purposes of the present document, the terms given in ETSI GS MEC 001 [i.1] and the following apply:
resource: object with a type, associated data, a set of methods that operate on it, and, if applicable, relationships to
other resources
NOTE: A resource is a fundamental concept in a RESTful API. Resources are acted upon by the RESTful API
using the Methods (e.g. POST, GET, PUT, DELETE, etc.). Operations on Resources affect the state of
the corresponding managed entities.
3.2 Symbols
Void.
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3.3 Abbreviations
For the purposes of the present document, the abbreviations given in ETSI GS MEC 001 [i.1] and the following apply:
API Application Programming Interface
BYOT Bring Your Own Transport
CRUD Create, Read, Update, Delete
DDoS Distributed Denial of Service
GS Group Specification
HATEOAS Hypermedia As The Engine Of Application State
HTTP Hypertext Transfer Protocol
HTTPS HTTP Secure
IANA Internet Assigned Numbers Authority
IETF Internet Engineering Task Force
ISG Industry Specification Group
JSON JavaScript Object Notation
MEC Multi-access Edge Computing
POX Plain Old XML
REST Representational State Transfer
RFC Request For Comments
RPC Remote Procedure Call
TCP Transmission Control Protocol
TLS Transport Layer Security
UE User Equipment
URI Uniform Resource Indicator
XML eXtensible Markup Language
4 Design principles for developing RESTful MEC
service APIs
4.1 REST implementation levels
The Richardson Maturity Model as defined in [i.3] breaks down the principal elements of a REST approach into three
steps.
All RESTful MEC service APIs shall implement at least Level 2 of the Richardson Maturity Model explained in
annex C.
It is recommended to implement Level 3 when applicable.
4.2 General principles
RESTful MEC service APIs are not technology implementation dependent.
RESTful MEC service APIs embrace all aspects of HTTP /1.1 (IETF RFC 7231 [1]) including its request methods,
response codes, and HTTP headers. Support for PATCH (IETF RFC 5789 [3]) is optional.
For each RESTful MEC service API specification, the following information should be included:
• Purpose of the API.
• URIs of resources including version number.
• HTTP methods (IETF RFC 7231 [1]) supported.
• Representations supported: JSON and, if applicable, XML.
• Response schema(s).
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• Request schema(s) when PUT, POST, or PATCH are supported.
• Links supported (Optional in Level 2 APIs).
• Response status codes supported.
Since the release of HTTP/1.1, major revisions have been introduced through HTTP/2 (IETF RFC 7540 [18]) including
binary serialization in place of textual, single TCP connection, full multiplexing, header compression and server push.
MEC system deployments may utilize HTTP/2. However, this is transparent to the RESTful MEC service APIs, as the
main semantic of HTTP has been retained in HTTP/2 thereby providing backwards compatibility. If HTTP/2 (IETF
RFC 7540 [18]) is supported, its use shall be negotiated as specified in section 3 of IETF RFC 7540 [18].
4.3 Entry point of a RESTful MEC service API
Entry point for a RESTful MEC service API:
• Needs to have one and exactly one entry point. The URI of the entry point needs to be communicated to API
clients so that they can find the API.
• It is common for the entry point to contain some or all of the following information:
- Information on API version, supported features, etc.
- A list of top-level collections.
- A list of singleton resources.
- Any other information that the API designer deemed useful, for example a small summary of operating
status, statistics, etc.
• It can be made known via different means:
- Client discovers automatically the entry point and meaning of the API.
- Client developer knows about the API at time of client development.
4.4 API security and privacy considerations
To allow proactive protection of the APIs against the known security and privacy issues, e.g. DDoS, frequency attack,
unintended or accidental information disclosure, etc. the design for a secure API should consider at least the following
aspects:
• Ability to control the frequency of the API calls (calls/min), e.g. by supporting the definition of a validity time
or expiration time for a service response.
• Anonymization of the real identities.
• Authorization of the applications based on the sensitivity of the information exposed through the API.
5 Documenting RESTful MEC service APIs
5.1 RESTful MEC service API template
Annex D defines a template for the documentation of RESTful MEC service APIs. Examples how to use this template
can for instance be found in ETSI GS MEC 011 [i.6] and ETSI GS MEC 012 [i.7].
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5.2 Conventions for names
5.2.1 Case conventions
The following case conventions for names and strings are used in the RESTful MEC service APIs.
1) UPPER_WITH_UNDERSCORE
All letters of a string are capital letters. Digits are allowed but not at the first position. Word boundaries are
represented by the underscore "_" character. No other characters are allowed.
EXAMPLE 1:
a) ETSI_MEC_MANAGEMENT.
b) MULTI_ACCESS_EDGE_COMPUTING.
2) lower_with_underscore
All letters of a string are lowercase letters. Digits are allowed but not at the first position. Word boundaries are
represented by the underscore "_" character. No other characters are allowed.
EXAMPLE 2:
a) etsi_mec_management;
b) multi_access_edge_computing.
3) UpperCamel
A string is formed by concatenating words. Each word starts with an uppercase letter (this implies that the
string starts with an uppercase letter). All other letters are lowercase letters. Digits are allowed but not at the
first position. No other characters are allowed. Abbreviations follow the same scheme (i.e. first letter
uppercase, all other letters lowercase).
EXAMPLE 3:
a) EtsiMecManagement.
b) MultiAccessEdgeComputing
4) lowerCamel
As UpperCamel, but with the following change: The first letter of a string shall be lowercase (i.e. the first
word starts with a lowercase letter).
EXAMPLE 4:
a) etsiMecManagement;
b) multiAccessEdgeComputing.
5.2.2 Conventions for URI parts
5.2.2.1 Introduction
Based on IETF RFC 3986 [9], the parts of the URI syntax that are relevant in the context of the RESTful MEC service
APIs are as follows:
• Path, consisting of segments, separated by "/" (e.g. segment1/segment2/segment3).
• Query, consisting of pairs of parameter name and value (e.g. ?org=etsi&isg=mec, where two pairs are
presented).
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5.2.2.2 Path segment naming conventions
a) Each path segment of a resource URI which represents a constant string shall use lower_with_underscore.
Only letters, digits and underscore "_" are allowed.
EXAMPLE 1: etsi_mec_management
b) If a resource represents a collection of entities, and the last path segment of that resource's URI is a string
constant, the last path segment shall be plural.
EXAMPLE 2: …/prefix/api/v1/users
c) If a resource is not a task resource and the last path segment of that resource's URI is a string constant, the last
path segment should be a (composite) noun.
EXAMPLE 3: …/prefix/api/v1/users
d) For resources that are task resources, the last path segment of the resource URI should be a verb, or at least
start with a verb.
EXAMPLE 4:
…/app_instances/{appInstanceId}/instantiate
…/app_instances/{appInstanceId}/do_something_else
e) A name that represents a URI path segment or multiple URI path segments in the API documentation but
serves as a placeholder for an actual value created at runtime (URI path variable) shall use lowerCamel, and
shall be surrounded by curly brackets.
EXAMPLE 5: {appInstanceId}
f) Once a variable is replaced at runtime by an actual string, the string shall follow the rules for a path segment or
sequence of path segments (depending on whether the variable represents a single path segment or a sequence
thereof) defined in IETF RFC 3986 [9]. IETF RFC 3986 [9] disallows certain characters from use in a path
segment. Each actual RESTful MEC service API specification shall define this restriction to be followed when
generating values for path segment variables, or propose a suitable encoding (such as percent-encoding
according to IETF RFC 3986 [9]), to escape such characters if they can appear in input strings intended to be
substituted for a path segment variable.
5.2.2.3 Query naming conventions
a) Parameter names in queries shall use lower_with_underscore.
EXAMPLE 1: ?isg_name=MEC
b) Variables that represent actual parameter values in queries shall use lowerCamel and shall be surrounded by
curly brackets.
EXAMPLE 2: ?isg_name={chooseAName}
c) Once a variable is replaced at runtime by an actual string, the convention defined in clause 5.2.2.2 item f)
applies to that string.
5.2.3 Conventions for names in data structures
The following syntax conventions apply when defining the names for attributes and parameters in the RESTful MEC
service API data structures.
a) Names of attributes / parameters shall be represented using lowerCamel.
EXAMPLE 1: appName.
b) Names of arrays and maps (i.e. those with cardinality 1.N or 0.N) shall be plural rather than singular.
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EXAMPLE 2: users, mecApps.
c) The identifier of a data structure via which this data structure can be referenced externally should be named
"id".
d) Each value of an enumeration types shall be represented using UPPER_WITH_UNDERSCORE.
EXAMPLE 3: NOT_INSTATIATED.
e) The names of data types shall be represented using UpperCamel.
EXAMPLE 4: ResourceHandle, AppInstance.
5.3 Provision of an OpenAPI definition
An ETSI ISG MEC GS defining a RESTful MEC service API should provide a supplementary description file (or
supplementary description files) compliant to the OpenAPI specification [i.14], which inherently include(s) a definition
of the data structures of the API in JSON schema or YAML format. A description file is machine readable facilitating
content validation and autocreation of stubs for both the service client and server. A link to the specific repository
containing the file(s) shall be provided. All API repositories can be accessed from https://forge.etsi.org. The file (or
files) shall be informative. In case of a discrepancy between supplementary description file(s) and the underlying
specification, the underlying specification shall take preced
...