[MidoNet-dev] L4-7 Service Platform document on Wiki

Dan Mihai Dumitriu dan at midokura.com
Mon Feb 11 12:42:18 UTC 2013


After a couple of brainstorming chats, I believe we have a strawman
proposal for how to incorporate flow redirection into our current model,
using the chain & rule framework, so that this is an incremental addition
to our model. (kaizen! ;-)

We introduce a new type of rule target which sends the flow to a port and
interrupts 'normal' processing, where normal depends on the type of virtual
device, i.e. routing for a vrouter and learning switching for a vswitch.
 (This just came to mind, but note that in the case of a vswitch, ports
attached to services should be marked as non-flooding, so that they don't
normally participate in the learning switch.) Flows coming back into the
virtual topology from a service would enter via another vport. (Pino, after
talking with Stephen some more, we thought it might be too complex to
reenter the virtual topology in the same chain, and with the same original
ingress vport.)

Another thing which comes to mind, however, is that if we want to do
service chaining, this model is not sufficient, because each time the flow
enters the virtual topology, from a service, it has lost the context of the
original flow.  I have one extremely half-baked idea that could help here.
 If we had extra space in the tunnel id, e.g. if we used GRE with 64 bit
keys, or STT, could we use 32 of those bits to identify the original flow?
 That way, even if a flow passed through a service and was modified, we can
still identify it when it comes back into MN, and thus can enforce some
order of services.  (I'm still thinking of how this might work; suggestions
are welcome.)

For the elasticity aspect, how about we introduce a level of indirection at
the vport level, something like a 'group' vport, which will dispatch to one
of a set of vports, based on flow hash.

What do y'all think?

Cheers,
Dan


On Thu, Feb 7, 2013 at 11:19 PM, Dan Mihai Dumitriu <dan at midokura.com>wrote:

> Hi Stephen,
>
> This is a great writeup!  I believe that we must take MidoNet into such a
> direction in order to provide the services needed by IaaS cloud users.
>  Please find my [yet incomplete because I'm falling asleep] comments below.
>
> Cheers,
> Dan
>
>
>    - Goals
>    - AWS
>    - Cisco 1000v vPath
>       - flow redirection
>          - allows VEM to direct traffic toward the service via tunneling
>          - what is required?  match() -> encapsulate to target (host,
>          vport) ?
>       - decision caching
>          - service node made a decision (think firewall) on a particular
>          flow and then download the flow entry to a target VEM (normally the VEM who
>          forwards the traffic to the service node)
>          - I suppose that a service node could be looking deeper than L4,
>          but that the decision must match a flow using fields up to L4.
>          - how is a flow identified?  still only by L2-L4 fields?
>       - service chaining
>          - enforce a traffic flow evaluation order upon which a flow
>          should traverse
>          - I don't quite get this one.
>        - vCEF
>       - what is SDDC?
>       - does this vCEF method use tunneling?
>       - I didn't quite understand what is unique about vCEF, other than
>       normalizing the
>    - Quantum Service Insertion
>       - Routed Mode
>          - How are flows specified?  Matching on IP?
>       - Floating/In-path Mode
>          - in this mode, the service is 'transparent' to the traffic?
>       - Redirected/Out-of-path Mode
>    - MidoNet Elastic Network Services Framework
>       - Service Launching Model
>          - case B sounds ideal, but I can see the potential pitfalls of
>          this approach.  the implementation for each cloud stack could end up being
>          somewhat different.  That said, it's not impossible, and may not be that
>          intrusive.  For example, OpenStack has a pluggable 'scheduler' which
>          chooses where VMs are launched.  The service platform could include such a
>          plugin in order to control where service VMs are launched.  (CloudStack may
>          have something as well.)  Furthermore, libraries like jclouds can be used
>          to abstract the cloud API (EC2 or OS or CS).  This is all very superficial
>          commentary, however. :)
>       - Service registration and configuration translation
>          - this sounds like what i've been thinking about, and somewhat
>          similar to the way that CloudStack manages its router virtual machine,
>          except that in the CS case the CS agent calls into the VM, rather than vice
>          versa.
>       - Service Insertion Model
>          - Flow Redirection
>             - "This flow should be installed as a wildcard flow into the
>             affected virtual router"
>                - we currently don't have a way to insert such low level
>                flows into the virtual router.
>                - we do have rule chains which can do flexible matching,
>                and I suppose we could make some kind of actions that do a redirect,
>                bypassing the routing stage.
>              - Elastic Service Insertion
>             - "Since we use the same hash function and extract the same
>             fields to perform the calculation, different ingress node will still yield
>             the same result"
>                - Is that really true? Can this decision always be
>                deterministic?
>             - What's the distinction between ECMP and VLB in this case?
>           - Flow Entries Management
>          - b is something like Direct Server Return
>          http://www.slideshare.net/cwestin63/l3-dsr-lspepresentation20120119
>           ?
>          - I suppose that an L7 LB would be in case c?
>          - (I got lost on much of the rest of this section)
>       - Management Interface
>       - Configuration Management
>       - Dynamic States Management
>          - indeed, makes sense; we'll have to hack up haproxy or some
>          such thing.  I wonder if nginx makes this easier.
>       - Elasticity
>    - Example Application: MidoNet Elastic Load Balancing (MNELB)
>       - Operating Model
>          - VIP is better than DNS name! :)
>       - Launch Model
>          - image maintenance
>             - the image may need to be tweaked for each stack (OS vs CS)
>           - Elasticity Management
>       - Traffic Flow
>          -
>       - HTTPS Flows
>          - SSL offloading and HTTPS with L7 load balancing
>          - Regarding the "session ID" in SSLv3, in this case where is the
>          SSL engine running?
>             - Is this assuming that the target server would do the actual
>             SSL?
>           - Appendix 1: What if our ingress router cannot handle that
>    many flows?
>       - Why is the exact match unscalable?  Is that because the kmod flow
>       hashtable cannot scale?  How large do we think it can scale?  Is it just a
>       matter of memory use?
>       - Does TCAM really solve our problem?  It seems that in order to
>       'virtualize' the network, we really do need to run a simulation per flow.
>        That's because we are using information that is not available in the tcam
>       to make the decision about what to do with the flow.
>          - We would not be able to do stateful flow processing in the
>          ingress edge.
>          - Rather, probably what we'd do is forward the flow to a
>          'service node' which would run the simulation, and then push back the flow
>          decision to the ingress edge, potentially bypassing the service node,
>          assuming only stateless L2-L4 processing needed to be done.
>
>
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