CS 91: Cloud Systems & Datacenter Networks Misc. Topics

Transcription

1 CS 91: Cloud Systems & Datacenter Networks Misc. Topics

2 Announcements EC2 username / passwords Lab today

3 Spanner Enables external consistency, based on wall- clock Gme

4 ConvenGonal Wisdom Don t use clocks

5 ConvenGonal Wisdom Don t use clocks Node 1 Node 2

6 ConvenGonal Wisdom If we look at the Gmestamps, the value should be 2. If we look at the order Don t in which use clocks the events really occurred, the value might be 7 (if A = 7 overwrote A = 2). Node 1 Node 2 Write A = 2 (5:00) Write A = 7 (4:30) What should the value of A be?

7 Spanner Go to great lengths to keep clocks in sync as closely as possible. Key insight: SGll can t trust any node to know exactly what Gme it is. Can trust them to be within a small window!

8 Spanner Node 2 s write must use a Gmestamp that comes a\er node 1 s write because it happened a\er it. Uncertainty limits parallelism. Write A = 2 (5:00 +/- 0:01) Node 1 Node 2 Prevent anyone from accessing A during uncertainty period. (Don t release lock.) Write A = 7 (5:02 +/- 0:01)

9 Time Uncertainty (ms) a\er sync Figure 6

10 (Rejoicing) Only four papers le\!

11 So far Course units VirtualizaGon Datacenter Networking Consistency Failures & ReplicaGon Data Storage & Retrieval Throughout: performance, scalability

12 What s missing? 1. Security Risks of shared infrastructure? Keeping bad network traffic out ByzanGne faults 2. ElasGcity Scale available equipment up or down on demand Reduce OPEX

13 1. Security CombinaGon of policy and mechanism Difficult to generalize. My ajempt: ensuring that inputs comply with policy Lots of ways to do this. We ll congnue our focus on cloud infrastructure: middleboxes

14 End- to- end principle End- to- end Arguments in System Design ( 81) Devices in the network should be simple Routers / switches look at small porgon of packet Make quick decision about what to do Complex funcgonality belongs at endpoints More processing power at client / server

15 End- to- end example: reliability

16 End- to- end principle Advantages Keeps the network a basic transfer fabric Network devices are more scalable (no per- flow state) Network devices are faster, they have less work to do Disadvantages Despite E2E, people o\en add smart/complex devices to the network all the Gme. Why?

17 End- to- end principle Advantages Keeps the network a basic transfer fabric Disadvantages Endpoints can t o\en see aggregate traffic Network devices are more scalable (no per- flow state) Network devices are faster, they have less work to do Might need to differengate or isolate traffic before it reaches an endpoint O\en easier to enforce policies in fewer locagons

18 Middleboxes Smart / non- simple network device Not a switch or router Not a server or client machine (Anything else) any intermediary box performing funcgons apart from normal, standard funcgons of an IP router on the data path between a source host and desgnagon host. (RFC 3234) Among other things, they do the type of stuff that we did to packets in lab 2.

19 Middlebox Examples Network Address TranslaGon (NAT) Use one IP address for many machines Load balancer Send traffic to a good / fast server WAN OpGmizer Compress & cache data between remote sites

20 Middlebox Examples: Security Firewall Look at packet headers, make policy decision Intrusion detecgon / prevengon system Look for packet pajerns, deep packet inspecgon

21 InteresGng Problems How many middleboxes are needed? How do we ensure that middleboxes intercept all the traffic they re supposed to? CloudNaaS: Lets users build a custom network infrastructure w/ middleboxes

22 2. ElasGcity Recall: Two costs associated providing cloud servers. CAPEX, OPEX The amount of stuff you buy (CAPEX) determines your overall capacity. The amount of stuff you re using right now determines your OPEX.

23 Suppose you have a public cloud What percentage of your equipment should you keep online? Tradeoff: response Gme vs. cost Ideally, systems could enter low- power state, rapidly power up again when needed

24 Power ProporGonality The amount of power a machine uses is proporgonal to the amount of work it s doing Hardware is gerng bejer, but sgll not there ElasGcTree: Saving Energy in Data Center Networks

25 Preview: Remaining Papers Hey, You, Get Off of My Cloud: Exploring InformaGon Leakage in Third- Party Compute Clouds Just how isolated are public cloud services? PracGcal ByzanGne Fault Tolerance Dealing with failures in which so\ware might be compromised, malicious, or other badness