Re: [Dime] WGLC #1 for draft-ietf-dime-load-02

["Gunn, Janet P" <[e-mail]>]

I am OK with the responses to my comments. 

 In cases where there is still a differnec of opinion, I do not have  a strong opinion either way.

Janet

-----Original Message-----
From: DiME [mailto:[e-mail]] On Behalf Of Maria Cruz Bartolome
Sent: Monday, June 27, 2016 3:19 AM
To: Steve Donovan <[e-mail]>; [e-mail]
Subject: Re: [Dime] WGLC #1 for draft-ietf-dime-load-02

Hello Steve, Janet,
See my comments below.
Thanks
/MCruz

-----Original Message-----
From: DiME [mailto:[e-mail]] On Behalf Of Steve Donovan
Sent: miércoles, 22 de junio de 2016 16:51
To: [e-mail]
Subject: Re: [Dime] WGLC #1 for draft-ietf-dime-load-02

I'll respond to both Maria Cruz and Janet's comments using Janet's email.

Regards,

Steve

On 6/21/16 11:16 AM, Gunn, Janet P wrote:
> Comments in line <JPG>
>
> -----Original Message-----
> From: DiME [mailto:[e-mail]] On Behalf Of Maria Cruz 
> Bartolome
> Sent: Monday, June 20, 2016 5:14 AM
> To: [e-mail]; [e-mail]
> Subject: Re: [Dime] WGLC #1 for draft-ietf-dime-load-02
>
> Hello all,
>
> I would like to provide some questions, proposed changes and typos, see in different sections to ease reading.
> Best regards
> /MCruz
>
>
> ===========  SOME QUESTIONS ===========:
>
> Appendix A.  Topology Scenarios
> Does it really make sense to keep an appendix that states:
>     "Nothing in this section should be construed to mean that a given
>     scenario is in scope for this effort, or even a good idea."
>
> I think we need to keep only the scenarios that are "in scope of this effort", what I understand as "suitable for load conveyance as stated in this draft".
> If some of them are not considered suitable by any reasons, I presume they should be removed.
> <JPG> Or note as (counter) examples of scenarios NOT suitable.</JPG>
SRD> I propose that we take out the above sentence.  It looks to me like
all of the scenarios are perfectly valid.
MCRUZ> Fine

>
> A.10.  Addition and removal of Nodes
> Shouldn't this part of the annex be in the regular body of the draft?
SRD> I agree this would be good in the body of the draft.  I'll move it
to the end of section 6.
MCRUZ> Fine

>
>
> =========== PROPOSED CHANGES ===========:
>
> Abstract:
>
> Now:
>     This document defines a mechanism for *sharing*  of Diameter load
>     information.
> Proposed:
>     This document defines a mechanism for *conveying* Diameter load
>     information.
>
> Reasoning:
> *Sharing" may be a bit misleading.
>
> <JPG> Agree. Conveying is better. </JPG>
SRD> Agreed
MCRUZ> Fine

>
> 1. Introduction:
> Now:
>    In particular, DOIC does not fulfill Req 24, which requires a
>     mechanism where Diameter nodes can indicate their *current load* , even
>     if they are not currently overloaded.  DOIC also does not fulfill Req
>     23, which requires that *nodes that divert traffic*  away from
>     overloaded nodes be provided with sufficient information to select
>     targets that are most likely to have sufficient capacity.
>
> Proposal:
> I think we need to include the exact requirement text from RFC7068, since the description you use does not keep the exact meaning.
> E.g. *current load* should be replaced by *load levels", *nodes that divert traffic*, in fact is *nodes with traffic diversion capability*.
> Better, just list requirements. If an interpretation is required, this is fine, but the original text is important to be kept:
> REQ 23: The solution MUST provide sufficient information to enable a load-balancing node to divert messages that are rejected or otherwise throttled by an overloaded upstream node to other upstream nodes that are the most likely to have sufficient capacity to process them.
> REQ 24: The solution MUST provide a mechanism for indicating load levels, even when not in an overload condition, to assist nodes in making decisions to prevent overload conditions from occurring.
>
> <JPG> Agree.  Itt would make sense to have a section, or even an 
> appendix, which lists the requirements, and notes whichare/are not 
> met. </JPG>
SRD> I'm okay with Maria Cruz's suggestion that we copy the requirements
text for 23 and 24 into the document and have made this change.  I'm not sure there is benefit to include a detailed, requirement by requirement analysis for the Load mechanism but I'm open to this if there is consensus that it is needed.  I would prefer that specific shortcomings based on unaddressed requirements are  brought forward.
MCRUZ> Fine

>
> 1. Introduction
>
> Now:
>    There are several other requirements in [RFC7068] that mention both
>     overload and load information that are only partially fulfilled by
>     DOIC.
>    [....]
>     This document defines a mechanism that addresses the load-related
>     requirements from RFC 7068.
>
> Proposal
> We need to list the requirements we refer to. They are not listed anywhere, right?
> I think we refer to following Requirements:
>
> REQ 1: The solution MUST provide a communication method for Diameter nodes to exchange load and overload information.
> REQ 2: The solution MUST allow Diameter nodes to support overload control regardless of which Diameter applications they support. Diameter clients and agents must be able to use the received load and overload information to support graceful behavior during an overload condition. Graceful behavior under overload conditions is best described by REQ 3.
> REQ 12: When a single network node fails, goes into overload, or suffers from reduced processing capacity, the solution MUST make it possible to limit the impact of the affected node on other nodes in the network. This helps to prevent a small- scale failure from becoming a widespread outage.
> REQ 34: The solution SHOULD provide a method for exchanging overload and load information between elements that are connected by intermediaries that do not support the solution.
>
> <JPG> Agree. See above comment. </JPG>
SRD> See my comment above.  The introduction is giving motivation for
why this mechanism is being defined.  I  think listing Req 23 and Req 24 is strong enough motivation.  Having a mention that there are other requirements that mention the need for load adds to that motivation.  I don't see the need to list those requirements in this document.  A reader can go to the requirements document to find then if needed.
MCRUZ> Fine

>
> 2. Terminology and abbreviations
>
> Now:
> Load
>        The *relative  capacity of a Diameter node*.  A low load level
>        indicates that the Diameter node is under utilized.  A high load
>        level indicates that the node is closer to being fully utilized.
>
> Proposed:
> Load
>        The* Diameter message processing  capacity of a node*.  A low load level
>        indicates that the Diameter node is under utilized.  A high load
>        level indicates that the node is closer to being fully utilized.
>
> Reasoning:
> I think using "relative" is misleading.
>
> <JPG> I do not like either. "Capacity" is what the node can do.
>
>   "Available capacity" is actually HIGH when there is a low load level, and LOW when there is a high laod level.
>
> If you want to avoid "Utilization", which implies an explicit 
> calculation, you could say "the relative usage of the Daimeter message 
> processing capacity'" </JPG>
SRD> I'm good with Janet's suggestion.


>
> 4.1
> Now:
>     Second, Overload information, in the form of a DOIC Overload Report
>     (OLR) [RFC7683] indicates an explicit request for action on the part
>     of the reacting node.  That is, the OLR requests that the reacting
>     node reduce the offered load -- the actual traffic sent to the
>     reporting node after overload abatement and routing decisions are
>     made -- by an indicated amount *or to an indicated level *.
>
> Proposed:
>     Second, Overload information, in the form of a DOIC Overload Report
>     (OLR) [RFC7683] indicates an explicit request for action on the part
>     of the reacting node.  That is, the OLR requests that the reacting
>     node reduce the offered load -- the actual traffic sent to the
>     reporting node after overload abatement and routing decisions are
>     made -- by an indicated amount *(by default, or other optional 
> abatement algorithms).*
>
>    - Or remove everything after "amount".
>
> <JPG> RFC7683 is clear that the Overload Report may be used to trigger 
> EITHER a loss based algorithm, or a different (e.g. rate based) 
> algorthm.  So the summary here should not be restricted to a 
> loss-based description.  Perhaps "--by an indicated amount (by 
> default), or as prescribed by the selected abatement algorithm."
> </JPG>
SRD> I've updated this based on Janet's suggestion.
MCRUZ> Fine

>
> 4.1
> Now:
>     None of this prevents a Diameter node from deciding to reduce the
>     offered load based on load information.   .
>
> Proposed
>    (remove)
>
> Reasoning:
> This sentence is not properly linked to previous paragraph and it is 
> covered by previous paragraph already
>
> <JPG> OK with this, though not sure it is necessary to delete.</JPG>
SRD> This sentence adds emphasis to the point that a similar result can
happen between load and overload, leading into the next sentence outlining the fundamental difference between the two.  I don't see the harm in leaving it, even if what is says is implied by the previous paragraph.
MCRUZ> My problem with the sentence is that it is not straight forward to what refers "none of this". The reader will look above to check what it refers to... and it seems to be the whole paragraph, i.e. the differences between load and overload. But this sentence refers again to something that is mentioned above. Then, I think the sentence, as it is, is misleading that turns reading a bit unease. 

>
> 4.2
> Now:
>     Req 24 discusses how Diameter load information might be used when no
>     overload condition currently exists.  Diameter nodes can use the load
>     information to make decisions to try to avoid overload conditions in
>     the first place.  Normal load-balancing falls into this category.  A
>     node might also take other proactive steps to reduce offered load
>     based on load information, so that the loaded node never goes into
>     overload in the first place.
>
> Proposed:
>     Req 24 discusses how Diameter load information might be used when no
>     overload condition currently exists.  Diameter nodes can use the load
>     information to make decisions to try to avoid overload conditions in
>     the first place.  Normal load-balancing falls into this category, but
>     the diameter node can  take other proactive steps as well.
>
> <JPG> Agree </JPG>
SRD> Agreed.
MCRUZ> Fine

>
> 4.2
> Now
>     If the loaded nodes are Diameter servers (or clients in the case of
>     server-to-client transactions), both of these uses are most
>     effectively accomplished  by a Diameter node that performs server
>     selection.
>
> Proposed:
>     If the loaded nodes are Diameter servers (or clients in the case of
>     server-to-client transactions), both of these *load information* uses *should
>     be*  accomplished  by a Diameter node that performs server
>     selection.
>
> Reasoning:
>    Diverting traffic can only be performed by a node that performs server selection, or?
>
> <JPG> Agree in principle, but I think that "..both of these uses of 
> laod information should be ..." reads better than  "... both of these 
> load information uses should be ...". </JPG>
SRD> Changed to:

         both of these uses of load information should
         be accomplished by a Diameter node that performs server selection.
MCRUZ> Fine

>
> 5.
> Now
>     The second big difference between DOIC and Load is visibility of the
>     DOIC or Load information within a Diameter network.  DOIC information
>     is sent end-to-end resulting in the ability of all nodes in the path
>     of the answer message that carries the OC-OLR AVP to act on the
>     information.  The DOIC overload reports much remain in the message
>     all the way from the reporting node to the node that is the target
>     for the answer message.
>
>     For the Load mechanism there are two types of load reports.
>
>     The first is the load of the endpoint sending the answer message.
>     This load report is carried end-to-end to enable any nodes that make
>     server selection decisions to use the load status of the sending
>     endpoint as part of  the server selection decision.
>
>     The second type of load report is a peer report.  This report is used
>     by Diameter nodes as part of the logic to select the next hop
>     Diameter node and, as such, do not have significance beyond the peer
>     node.  These load reports are removed by the first supporting
>     Diameter node to receive the report.
>
> Proposed:
>     The second big difference between DOIC and Load is visibility of the
>     DOIC or Load information within a Diameter network.  DOIC information
>     is sent end-to-end resulting in the ability of all nodes in the path
>     of the answer message that carries the OC-OLR AVP to act on the
>     information, *although only one node can actually consume the report*.  The DOIC overload reports much remain in the message
>     all the way from the reporting node to the node that is the target
>     for the answer message.
SRD> How about "although only one node actually reacts to the report",
changing consume to react.
MCRUZ> I think "consume" is better since it implies that from then on the report is removed.

>
>     *However,* for the Load mechanism there are two types of load reports *and only the
>      first one is transmitted end-to-end*.
SRD> This is covered in the following paragraphs.
MCRUZ> Yes, but I think we need an introduction for the analysis below, in order to understand we are going to compare. Trying to ease reading.

>
>     The first is the load of the endpoint sending the answer message.
>     This load report is carried end-to-end to enable any nodes that make
>     server selection decisions to use the load status of the sending
>     endpoint as part of  the server selection decision. *More than one 
> node may make use of the load information received*
SRD> How about:

    Unlike with DOIC, more than one node may make use of the load information received.
MCRUZ> Fine.

>
>     The second type of load report is a peer report.  This report is used
>     by Diameter nodes as part of the logic to select the next hop
>     Diameter node and, as such, do not have significance beyond the peer
>     node.  These load reports are removed by the first supporting
>     Diameter node to receive the report.
>
> <JPG> Slightly different comment.  I think the phrase " The DOIC 
> overload reports much remain in the message..." is a typo and should 
> be " The DOIC overload reports must (or MUST?) remain in the 
> message.."  <?JPG>
SRD> Yes, it was meant to be must but I think it is better to remove the
word altogether, leaving:

       The DOIC overload reports remain in the message all the way from the
       reporting node to the node that is the target for the answer message.
MCRUZ> Fine

>
> 5.
> Now
>    The goal is make it possible to use both the load values received as
>     a part of the Diameter Load mechanism and weight values received as a
>     result of a DNS SRV query.  As a result, the Diameter load value has
>     a range of 0-65535.  This value and DNS SRV weight values are then
>     used in a distribution algorithm similar to that specified in
>     [RFC2782].
>
> Comments:
> In order to have an efficient load balancing algorithm, it is not enough for the reacting node (for the node in charge of load balancing) to know the Load of each server, but it needs to know the load in relation to each server capacity. Unless we do so, the Load value of a server can't be compared with the Load of a Server with a different weight.
> Then, in my opinion, we need to find a way to provide a Load value that is in fact comparable with the rest of the Load values of the servers in the group.
> Reflecting a bit longer on this, I think we need then to define a group of servers in the load-balancing group, like a load-balancing context, and then, for all servers in such a group we need to provide a relative value of dynamic Load.
>
> <JPG> Agree with the thought- if "Little Server" is 30% utilized and 
> "Big Server" is 50% utilized, it still makes sense to send more 
> traffic to Big Server.  But I am not sure if that is withn the scope 
> of this document. </JPG>
SRD> I don't understand the concern.  The load values supplied will be
input into the route selection algorithm as specified in RFC2782.  If a node isn't getting enough traffic it will change its load value to a lower value and will start getting more traffic.
MCRUZ> Unless the LOAD info provided is in fact a value that represents the available capacity, then the load balancing will not select the less loaded server. Being able to select the less loaded server is the whole purpose of this mechanism, then we need to find a way to provide a LOAD value from different servers that we are able to compare, i.e. the value provide must indicate the available capacity regardless the static capacity of each server. 
Providing an example, let me use dynamic Load (say DL) in % (100% is totally loaded) that I found it easier for calculation:
- Server1: weight=1500; DL= 2%
- Server2: weight=55000; DL= 70%
Then, if we only use DL in the LB algorithm, obviously Server 1 seems to be clearly less loaded, but however, taking into account its weight is much smaller it may be the other way around. In fact, if traffic is redirected to this server, it may get overloaded rapidly (due to its small capacity).
One possible way to calculate the relative DL is  to divide it by the weight, then for this example:
- Server1 RDL= 10000 * (2/1500) = 13.33
- Server2 RDL= 10000 * (70/55000) = 12.73 (I multiplied by 10000 simply to get rid of the decimals for our discussion).
Then, we actually find out that available load for both servers is pretty similar. In fact, in this case, a correct load balancing should select Server2 as the less loaded server instead of server1.
My proposal is to consider this reflection in the draft, and then make a clear distinction between dynamic load (DL) and RELATIVE DL. We need to provide the RDL in the message, not DL.


>
> 5.
> Now
>     The load report includes the relative load of the sending node.  This
>     relative load is specified in a manner consistent with that defined
>     for DNS SRV [RFC2782].
>
> Proposed:
>     The load report includes a value to identify the load of the sending node,
>    specified in a manner consistent with that defined
>     for DNS SRV [RFC2782].
>
> <JPG> Agree. </JPG>
SRD> I don't understand the need for this change.
MCRUZ> Using "relative" is misleading unless we clarify "relative to what".

>
> 5.
> Now:
> The distribution algorithm used by Diameter nodes supporting the
>     Diameter Load mechanism is an implementation decision but it needs to
>     result in similar behavior as the algorithm specified in [RFC2782].
>
> Proposed:
> The distribution algorithm used by Diameter nodes supporting the
>     Diameter Load mechanism is an implementation decision but it needs to
>     result in similar behavior as the algorithm *described
>     for the use of weigth values in* [RFC2782].
>
> <JPG> Agree in principle. NIT- replace "similar behavior as" with 
> "similar behavior to", and repalce "weigth" with "weight". </JPG> (End 
> of my comments)
SRD> Agreed.
MCRUZ> Fine

>
>
> 5.1
> Now:
>    If Agent A4 supports the Load mechanism then it will verify that the
>     load information received is valid.  For a HOST load report this is
>     achieved by matching the identity included in the load information
>     with the identity of the host node from which the answer message was
>     received.
>
> Comments:
> A4 behaviour should be defined generically. In the example, we know S[n] is a peer of A4, but generically A4 will not know it when receiving a HOST report.
> Then, for an AgentX the HOST load report is valid as long as it is responsible for server selection, as explained for A1 below:
> A1's actions depend on whether A1 is
>     responsible for doing server selection.  If A1 is not doing server
>     selection then A1 ignores the HOST load report.  If A1 is responsible
>     for doing server selection then it stores the load information for
>     S[n] in its routing information for the handling of subsequent
>     request messages.  In both cases A1 leaves the HOST report in the
>     message
SRD> Agreed.  The section now looks as follows:

    If Agent A4 supports the Load mechanism then A4's actions depend on
    whether A4 is responsible for doing server selection.  If A4 is not
    doing server selection then A4 ignores the HOST load report.  If A4
    is responsible for doing server selection then it stores the load
    information for S[n] in its routing information for the handling of
    subsequent request messages.  In both cases A4 leaves the HOST report
    in the message.

       Note: If A4 does not support the Load mechanism then it will relay
       the answer message without doing any processing on the load
       information.  In this case the load information AVPs will be
       relayed without change.

    A4 then calculates its own load information and inserts load
    information AVPs of type PEER in the message before sending the
    message to A1.

MCRUZ> Fine

> 6.1.1
> Now:
>     The method for determining the load value included in the load report
>     is an implementation decision.
>
> Comments:
> In line to comment above, I agree it should be implementation specific, but we need to provide some guidance to be able to provide a value that could be used to achieve a successful load balancing.
SRD> See my comment above about DNS SRV algorithm.
MCRUZ> This is related to my comment above to 5, but to the part related to a way to provide a LOAD value that represents the available capacity of a server, taking into account its static capacity.

>
>
> 6.2
> Now:
>     If the Diameter node is responsible for doing server selection then
>     it SHOULD save the load value included in the Value AVP included in
>     the Load AVP of type HOST in its routing information.
>
> Proposed:
>     If the Diameter node is responsible for doing server selection then
>     it SHOULD save the load value included in the Value AVP included in
>     the Load AVP of type HOST.
>
> Reasoning:
> It is a bit misleading to state that is should be stored "in its routing information". It has to be used for server selection, regardless "how" and "where" it is stored.
SRD> This is based on the definition of routing information in section 2.
>
> 7.3
> Now:
>     The Load-Value AVP (AVP code TBD3) is of type Unsigned64.  It is used
>     to convey relative load information about the sender of the load
>     report.
>
> Comments:
> *Relative load*
> It seems it refers to what I commented before, about the "relative dynamic load", in that comment it is relative to the weight.
> But as the draft is now, I think it is misleading, since it is not clear to what it refers.
>
>
> 7.3
> Now:
>     The Load-Value AVP is specified in a manner similar to the weight
>     value in DNS SRV ([RFC2782]).
>
>     The Load-Value has a range of 0-65535.
>
>     A higher value indicates a lower load on the sending node.  A lower
>     value indicates that the sending node is heavily loaded.
>
>        Stated another way, a node that has zero load would have a load
>        value of 65535.  A node that is 100% loaded would have a load
>        value of 0.
>
> Comments:
> I think it could be easier to use a %. It is more straight forward to figure out what it means.
SRD> Percentage can be mapped to the range 0-65535 if that is the
internal implementation decision.  The goal here is to be consistent with RFC2782.
MCRUZ> Why do we need to keep consistency to that RFC? I think it is clearer to use a percentage, it is more straight forward to identify the available load we refer to.
E.g. 50% loaded, using SRV is 32767,5;  25% is 49151,25;  and so on.  
In the mechanism we are defining we do not have the need to keep using a complex value like this one, when we can simply use 0 to 100%, 0 (totally available), 100 (totally loaded).
In fact, this is in line to the definition in the doc:

Load
        The* Diameter message processing  available capacity of a node*.  A low load level
        indicates that the Diameter node is under utilized.  A high load
        level indicates that the node is closer to being fully utilized.


>
>
>
> =========== TYPOS========:
>
> 2. Terminology and abbreviations
>
>     Routing Information
>
>        Routing Information - Routing information referred to in this
>        document can include the Routing and Peer tables defined in RFC
>        6733.  It can also include other implementation specific tables
>        used to store load information.  This document does not define the
>        structure of such tables.
>
> Remove *Routing information* duplicated sentence.
SRD> I think it reads better as is.
>
> 4.1
> At any given time that load *maybe*  effectively
>     zero
> *May be*
SRD> Agreed.
>
> 5.1
> Because the load report is *an* HOST load report, A4 leaves the load
>     report in the message it relays.
SRD> This was addressed by the change to A4 wording above.
>
> 5.1
>     A1 then calculates its own load information and inserts load
>     information AVPs of type PEER in the message before sending the
>     message to *A1*
>
>    *A1* should be C
SRD> Agreed.
>
> 6.1.1
>        For instance, if the only consumer of the load reports is the
>       * endpoints peer* then the endpoint can choose to only include a load
>        report when the load of the endpoint has changed by a meaningful
>        percentage.  If there are consumers of the endpoint load report
>        other *thaen* the *endpoints peer* (this will be the case if other
>        nodes are responsible for server selection) then the endpoint
>        might choose to include load reports in all answer messages as a
>        way of ensuring that all nodes doing server selection get accurate
>        load information.
>
>       *endpoint's peer*
SRD> Agreed.
>
> 6.2
> A Diameter node MUST be prepared to process load reports of type HOST
>     *and* of type PEER
SRD> Agreed.
>
> 6.2
>        Note that the node needs to be able to handle messages with no
>        load reports, messages with just a PEER load report, messages with
>        just *an* HOST load report and messages with both types of load
>        reports.
SRD> Agreed.
>
>
>
> -----Original Message-----
> From: DiME [mailto:[e-mail]] On Behalf Of Jouni Korhonen
> Sent: martes, 24 de mayo de 2016 17:30
> To: [e-mail]
> Subject: [Dime] WGLC #1 for draft-ietf-dime-load-02
>
> Folks,
>
> This email starts the WGLC #1 for draft-ietf-dime-load-02. Please, review the document, post your comments to the mailing list and also insert them into the Issue Tracker with your proposed resolution.
>
> WGLC starts: 5/24/2016
>          ends: 6/7/2016 EOB PDT
>
> - Jouni & Lionel
>
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