Hi Rob, thanks for such a careful review. The -04 version posted a few seconds
ago should respond to your points, but we have inserted comments below.
On 19-Nov-21 07:27, Rob Wilton (rwilton) wrote:
Hi Authors, ANIMA, Toerless,
My AD review of draft-ietf-anima-asa-guidelines-03 is inline. I have also
attached a copy of my review because the IETF mailer likes to truncate my
review emails, so please check that you reached my signature for the full
review.
Toerless, please can you also update the Shepherd writeup to indicate that I'm
the responsible AD for this document.
The draft is well written, and mostly I have fairly minor comments to improve
the readability of the document in a few places. I also ran the document
through an automatic grammar checker, and the nits raised are at the end of my
review.
1. Would it be useful to have a terminology section for some of the acronyms,
to make
it easier for readers to refer back to? This could also help indicate where
the terms are defined? I'm happy to leave this entirely to the authors
discretion.
Yes, this seems useful (and should have been in RFC8993). Will add as an
Appendix.
1. Introduction
Another example is that an existing script for locally monitoring or
configuring functions or services on a router could be upgraded as an
ASA that could communicate with peer scripts on neighboring or remote
routers. A high-level API will allow such upgraded scripts to take
full advantage of the secure ACP and the discovery, negotiation and
synchronization features of GRASP. Familiar tasks such as
configuring an Interior Gateway Protocol (IGP) on neighboring routers
or even exchanging IGP security keys could be performed securely in
this way. This document mainly addresses issues affecting quite
complex ASAs, but the most useful ones may in fact be rather simple
developments from existing scripts.
2. In this example, is the assumption that the scripts are running on the
devices? It wasn't entirely clear to me. If so, perhaps reword the first part
of the paragraph to make this more clear?
Yes, done.
2. Logical Structure of an Autonomic Service Agent
As mentioned above, all but the simplest ASAs will need to suport
asynchronous operations. Not all programming environments explicitly
support multi-threading. In that case, an 'event loop' style of
implementation could be adopted, in which case each thread would be
implemented as an event handler called in turn by the main loop. For
this, the GRASP API (Section 3.3) must provide non-blocking calls and
possibly support callbacks. When necessary, the GRASP session
identifier will be used to distinguish simultaneous operations.
3. Various languages have better concurrency paradigms than threads and locks
(e.g., actors, futures, goroutines, etc). So, I think that you are using
threads here as a way to describe what operations are expected to be handled in
an asynchronous fashion, and to describe that using a fairly simple frame of
reference. You cover the single threaded case, but I didn't know whether it
would be helpful to indicate that other concurrency mechanisms can be used, or
perhaps that would just be obvious to folks who are familiar with them anyway
...
Well, I'd say "different concurrency paradigms" to avoid a value judgment, but
yes. We did cover this at more length in the API (RFC8992) so probably we should point to
that discussion. To avoid confusing text, I will move most of the text about asynchronous
operations into the section about the API.
(( From a quick glance at goroutines, I can only see a syntactic sugar
difference between _tcp_listen(listen_sock).start() in Python and go
_tcp_listen(listen_sock) in Go, for example. All these things are event loops
under the skin, anyway. ))
The logic of the main loop will depend on the details of the
autonomic function concerned. Whenever asynchronous operations are
required, extra threads will be launched, or events added to the
event loop. Examples include:
4. Suggest "extra threads may be launched, ...", since in some cases the
suggestion is
to reuse existing threads.
Ack
5. What are the examples of, i.e., are they examples of logic in the main loop,
or examples of asynchronous operations. Should this be clarified?
In the threaded model, they are threads.
4. Interaction with Non-Autonomic Components
An ASA, to have any external effects, must also interact with non-
autonomic components of the node where it is installed. For example,
an ASA whose purpose is to manage a resource must interact with that
resource. An ASA whose purpose is to manage an entity that is
already managed by local software must interact with that software.
For example, if such management is performed by NETCONF [RFC6241],
the ASA must interact directly with the NETCONF server in the same
node.
6. I presume that the ASA would be treated like any other NETCONF management client? Perhaps this is worth stating, and that it may need to coordinate configuration updates with other management clients.
Oh, it's so confusing to me that the NETCONF server (in the protocol sense) is
in the managed device, which in the big picture is not really a server at all.
Here's my attempt:
For example, if such management is performed by NETCONF
<xref target="RFC6241"/>,
the ASA must interact directly with the NETCONF server in the same node,
to avoid any inconsistency between configuration changes delivered
via NETCONF and configuration changes made by the ASA.
5. Design of GRASP Objectives
The general rules for the format of GRASP Objective options, their
names, and IANA registration are given in [RFC8990]. Additionally
that document discusses various general considerations for the design
of objectives, which are not repeated here. However, note that the
GRASP protocol, like HTTP, does not provide transactional integrity.
In particular, steps in a GRASP negotiation are not idempotent. The
design of a GRASP objective and the logic flow of the ASA should take
this into account. For example, if an ASA is allocating part of a
shared resource to other ASAs, it needs to ensure that the same part
of the resource is not allocated twice. The easiest way is to run
only one negotiation at a time. If an ASA is capable of overlapping
several negotiations, it must avoid interference between these
negotiations.
7. Is the alternative approach valid here, which is to design the GRASP Objectives such that they can be treated idempotently? I.e., where the receiver can detect that it is a duplicate request and ignore it. Generally, I find that to be a simple and robust way to do concurrent system design.
True, will add. For example, Toerless has a model that amounts to DNS-SD lookup
over GRASP. That is idempotent. But a shared resource objective can't be
idempotent, I don't think, because if A gives some resource to B, that needs to
be an atomic transaction.
3.3. Interaction with GRASP and its API states:
... The format and size
of the value is not restricted by the protocol, except that it must
be possible to serialise it for transmission in CBOR [RFC8949], which
is no restriction at all in practice.
and 5. Design of GRASP Objectives states:
The maximum size of the value field of an objective is limited by the
GRASP maximum message size. If the default maximum size specified by
[RFC8990] is not enough, the specification of the objective must
indicate the required maximum message size, both for unicast and
multicast messages.
A mapping from YANG to CBOR is defined by [I-D.ietf-core-yang-cbor].
Subject to the size limit defined for GRASP messages, nothing
prevents objectives using YANG in this way.
8. Does the description of the maximum message size conflict between section 3.3 and the two paragraphs in section 5?
Good catch. I will make the text consistent. If there's anything in GRASP that
we need to revisit, it's this. What I realised (and implemented) is that it
will work with pretty much any reasonable message size limit; it's just matter
of receive buffer size (and avoidance of buffer overrun bugs, of course).
Documented in
https://www.ietf.org/archive/id/draft-carpenter-anima-grasp-config-00.html
5. Design of GRASP Objectives
A mapping from YANG to CBOR is defined by [I-D.ietf-core-yang-cbor].
Subject to the size limit defined for GRASP messages, nothing
prevents objectives using YANG in this way.
9. Given that you are taking about size limits, would it be worth mentioning the YANG
CBOR SID encoding that allows for even more compact messages?
I see that SIDs are mentioned at least 156 times in the yang-cbor draft, so I
think we are covered.
6.2.2. Instantiation phase inputs and outputs
[Instantiation_target_parameters] that specifies which are the GRASP
objectives to be set to ASAs (e.g. an optimization target)
10. Did you mean set to, or perhaps set on, or sent to?
"sent to" (unless Laurent disagrees)
6.3. Operation phase
Modify ASAs managed resources: by updating the instance mandate
which would specify different set of resources to manage (only
applicable to decouples ASAs).
11. decouples ASAs => decoupled ASAs?
"decoupled"
During the Operation phase, running ASAs can interact the one with
the other:
12. Suggest => interact with other ASAs:
Yes
in order to exchange knowledge (e.g. an ASA providing traffic
predictions to load balancing ASA)
13. Suggest => to a load balancing ASA
Yes
During the Operation phase, running ASAs are expected to apply
coordination schemes
then execute their control loop under coordination supervision/
instructions
14. I wasn't really sure that I understand what was meant by the above.
We can simplify the text. The immediately following section describes this
better.
10. Robustness
It is of great importance that all components of an autonomic system
are highly robust. In principle they must never fail. This section
lists various aspects of robustness that ASA designers should
consider.
15. I would suggest rewording this paragraph to something like follows (with
an emphasis on recovery than trying to avoid failures):
It is of great importance that all components of an autonomic system
are highly robust. Although ASA designers should aim for the
component to never fail, it is more important to design the ASA to
assume that failures will happen and to gracefully recover from those
failures when they occur. Hence, this section lists various aspects
of robustness that ASA designers should consider.
Yes, excellent.
Appendix B. Example Logic Flows
16. Using a periodic timer is arguably better than a sleep loop (but
requires the code to be event based)
Right. sleep() is the simple-minded approach, actually. In Python,
I could use a combination of time.sleep() and time.monotonic()
to make a true periodic timer, even in threaded code, in a case
where it matters. We'll change the comment in the pseudocode.
17. Should the NEGOTIATOR thread exit when it has completed?
Yes. My brain has been unduly influenced by Python, where a thread
does exit if you drop out of the code. You can't write exit()
because that exits the whole shebang. Will clarify with a comment.
18. Minor nits from a grammar checking tool are below.
Will fix.
Thanks again,
Brian and co-authors.
Potential Spelling Errors:
successfull, suport, un-install
e.g. => e.g.,
Grammar Warnings:
Section: 1, draft text:
To achieve this objective, the autonomic networks ecosystem must include at
least a library of ASAs and corresponding GRASP objective definitions.
Warning: Apostrophe might be missing.
Suggested change: "networks'"
Section: 1, draft text:
However, for the present document, the basic definitions and goals for
autonomic networking given in [RFC7575] apply .
Warning: Don't put a space before the full stop.
Suggested change: "."
Section: 1, draft text:
Of course it also interacts with the specific targets of its function, using
any suitable mechanism.
Warning: The comma is probably missing here: course, it.
Suggested change: "course, it"
Section: 3.3, draft text:
Thus ASAs may operate without special privilege, unless they need it for other
reasons.
Warning: Did you forget a comma after a conjunctive/linking adverb?
Suggested change: "Thus,"
Section: 5, draft text:
Additionally that document discusses various general considerations for the
design of objectives, which are not repeated here.
Warning: Did you forget a comma after a conjunctive/linking adverb?
Suggested change: "Additionally,"
Section: 6.2, draft text:
having a piece of code available to run on a host and 2.
Warning: This sentence does not start with an uppercase letter.
Suggested change: "Having"
Section: 6.2, draft text:
having an agent based on this piece of code running inside the host.
Warning: This sentence does not start with an uppercase letter.
Suggested change: "Having"
Section: 6.2.1, draft text:
Additionally in this phase, the operator may want to set goals to autonomic
functions e.g. by configuring GRASP objectives.
Warning: Did you forget a comma after a conjunctive/linking adverb?
Suggested change: "Additionally,"
Section: 10, draft text:
In principle they must never fail.
Warning: The comma is probably missing here: principle, they.
Suggested change: "principle, they"
Section: 11, draft text:
Independently of this, interfaces between ASAs and the router
configuration/monitoring services of the node can be subject to authentication
that provides more fine grained authorization for specific services.
Warning: This word is normally spelled with hyphen.
Suggested change: "fine-grained"
Section: Appendix B, draft text:
Thus the ASA logic has two operating modes: origin and delegator.
Warning: Did you forget a comma after a conjunctive/linking adverb?
Suggested change: "Thus,"
Thanks,
Rob
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