1 CS 188/219 Scalable Internet Services Andrew Mutz October 8, 2015
2 For Today About PTEs Empty spots were given out If more spots open up, I will issue more PTEs You must have a group by today. More detail at end of this lecture. If you still need a group, come up front during halftime.
3 For Today Motivation Vertical Scaling Horizontal Scaling For Next Time...
5 Motivation After today s lecture you will understand what load balancing is, and and why the architecture depicted here allows cost effective and smooth scaling paths.
6 Motivation Suppose you ve built something the world is excited about. What do you do when your popularity doubles?...and doubles again. and again.
7 Motivation We ve mentioned buying bigger hardware and scaling up This is called vertical scaling This is easy to do, but hits limits We ve mentioned buying more servers and scaling out This is called horizontal scaling This is harder to do, but doesn t really have limits Today we will look at both.
8 Vertical Scaling Vertical scaling Use a server with more memory, more/faster cores, higher bandwidth, etc. On EC2, there are a few scaling paths T and M series: balanced mix of memory and CPU C series: emphasis on CPU R series: emphasis on memory How much bang do you get for your buck? Let s take a look...
9 Vertical Scaling We will use the same testing script from the last lecture Going to the homepage Waiting for up to 2 seconds Requesting a form to create a new community Waiting for up to 2 seconds Submitting the new community Requesting a form to create a new link submission Waiting for up to 2 seconds Submitting the new link Waiting for up to 2 seconds Delete the link Waiting for up to 2 seconds Delete the community
10 Vertical Scaling When we test we will have 12 phases, of 60 seconds each: Phase Users/sec Remember these are users, not requests. There will be many requests per user, and users stay for 5-10s. Deployed using nginx/passenger.
11 Vertical Scaling M3 Large Instance 2 vcpus 7.5 GB Memory SSD storage Responds well with 6 new users per second, but fails with 10 ~$100 a month
12 Vertical Scaling M3 X-Large Instance 4 vcpus 15 GB Memory SSD storage Responds well with 10 new users per second, but fails with 16 ~$200 a month
13 Vertical Scaling M3 XX-Large Instance 8 vcpus 30 GB Memory SSD storage Responds well with 16 new users per second, but fails with 20 ~$400 a month, end of the M series.
14 Vertical Scaling C3 4X-Large Instance 16 vcpus 30 GB Memory SSD storage Responds well with 20 new users per second, but fails with 25 ~$600 a month,
15 Load Balancing Vertical Scaling has its place, but horizontal scaling is generally preferable. For HTTP, this technique is referred to as load balancing. Basic idea: have many servers that can serve clients, and make them appear as a single endpoint to the outside world Users experience is the same, regardless of which machine ultimately serves the request.
16 Load Balancing Question: how can we make many servers able to serve clients? What if I do the following actions: GET /products POST /products GET /products If these requests are handled by three different servers, will the third request show the new product?
17 Load Balancing In order for load balancing to work, these servers must be stateless. This is generally accomplished by keeping the persistence layer separate from the application layer
18 Load Balancing on the Web Idea #1: HTTP Redirects Discussed in section 6.1 of the reading Implemented using multiple web servers with different domain names uses http status 301 or 302 to redirect users to a pool of possible hosts.
19 Load Balancing on the Web % nc 80 GET / HTTP/1.1 host: HTTP/ Moved Permanently Date: Wed, 15 Oct :08:22 GMT Server: Apache/ (Ubuntu) Location: Content-Type: text/html; charset=iso
20 Load Balancing on the Web Strengths? Weaknesses?
21 Load Balancing on the Web Strengths: Simple Complete control over load balancing algorithm. Location independent. Weaknesses: Visible to user: URL bar, bookmarks, etc. www will see a lot of load.
22 Load Balancing on the Web Idea #2: Round Robin DNS Discussed in section 4.1 of the reading When user s browser queries DNS for a list of IPs is returned. User s browser chooses which IP to connect to (generally the first listed)
23 Load Balancing on the Web % host has address has address has address has address has address % host has address has address has address has address has address
24 Load Balancing on the Web Strengths? Weaknesses?
25 Load Balancing on the Web Strengths: Easy Cheap Simple Weaknesses: Less control over balancing Modifying the list is inhibited by caching in the browser and proxies
26 Load Balancing on the Web Idea #3: Load Balancing Switch Discussed in section 4.1 of the reading AKA: TCP Load Balancing The idea: rewrite TCP packets to send them to the correct server Addresses, sequence numbers and checksums need to be rewritten on the fly Constructed using hardware (ASICs) to perform this fast Commercial products available: Cisco Content Services Switch Citrix Netscaler F5 Big IP
27 Load Balancing on the Web client -> switch : > IP D= S= LEN=60, ID= > TCP D=80 S=1421 Syn Seq= Len=0 Win=32120 switch -> client : > IP D= S= LEN=48, ID= > TCP D=1421 S=80 Syn Ack= Seq= Len=0... client -> switch : > IP D= S= LEN=40, ID= > TCP D=80 S=1421 Ack= Seq= Len=0... client -> switch : > IP D= S= LEN=154, ID= > TCP D=80 S=1421 Ack= Seq= Len= > HTTP GET /eb/images/ec_home_logo_tag.gif HTTP/1.0
28 Load Balancing on the Web switch -> server : > IP D= S= LEN=48, ID= > TCP D=80 S=1421 Syn Seq= Len=0 Win=32120 Options... server -> switch : > IP D= S= LEN=44, ID= > TCP D=1421 S=80 Syn Ack= Seq= Len=0... switch -> server : > IP D= S= LEN=154, ID= > TCP D=80 S=1421 Ack= Seq= Len= > HTTP GET /eb/images/ec_home_logo_tag.gif HTTP/1.0
29 Load Balancing on the Web server -> switch : > IP D= S= LEN=40, ID= > TCP D=1421 S=80 Ack= Seq= Len=0 switch -> client : > IP D= S= LEN=40, ID= > TCP D=1421 S=80 Ack= Seq= Len=0... server -> switch : > IP D= S= LEN=1500, ID= > TCP D=1421 S=80 Ack= Seq= Len= > HTTP HTTP/ OK switch -> client : > IP D= S= LEN=1500, ID= > TCP D=1421 S=80 Ack= Seq= Len= > HTTP HTTP/ OK
30 Load Balancing on the Web Strengths? Weaknesses?
31 Load Balancing on the Web Strengths: More control over which requests go to which servers Works fine with HTTPS Weaknesses: Constrains where the servers are Complicated
32 Load Balancing on the Web Idea #4: Load Balancing Proxy Also known as Layer 7 load balancing Terminate HTTP requests: act like a web server Issue back-end HTTP requests to real web servers to get responses. Many hardware products available: Citrix Netscaler BigIP F5 Most HTTP servers have modules to do this as well.
33 Load Balancing on the Web Strengths: Cleaner implementation than packet rewriting Weaknesses: Load balancer needs to be doing more work SSL is more complicated This is the most popular technique in use today. Technique #3 also used as well
34 Load Balancing on the Web Let s say you are designing a load balancing proxy You see every request go in and out. What algorithm would you choose for balancing between machines?
35 Load Balancing on the Web Let s say you are designing a load balancing proxy... You see every request go in and out. What algorithm would you choose for balancing between machines? Random Round robin Least number of connections Fastest response time Bandwidth per Server Based on URI (e.g. /images, or /cgi-bin) ELB uses Round Robin with cookie-based stickiness
36 Load Balancing on the Web Some interesting challenges come up when designing a load balancing proxy Detecting Server Failures Session persistence & affinity Connection pooling
37 Load Balancing on the Web Detecting Server Failures How do we know when a member of our pool has died? We can observe traffic: are requests being serviced? Some requests just take a long time. We can probe the server Various protocols ICMP ping: test network and kernel TCP connection set up: process is running HTTP HEAD: it s serving pages SNMP: server load
38 Load Balancing on the Web Session persistence & affinity Can we redirect users back to the same web server they used before? This can get us caching improvements A few options: Affinity based on client IP address Client IPs change & IPs can be shared HTTP Cookie Works, but needs proxy configuration Session ID in URL Hard to parse out in a load balancer ( &SID=01234&...) Your sessions are in your URL??
39 Load Balancing on the Web Connection Pooling We re used to the idea that one client reuses a TCP connection for many HTTP requests. We can reuse this mechanism for distinct clients Saves on repeated TCP setup Reduce idle waiting on server for reads and writes
40 Load Balancing on the Web Common Load Balancers Hardware Software F5 Big IP Apache Citrix Netscaler HAProxy Cisco Varnish Pound Squid Nginx...
41 Load Balancing on the Web Amazon Elastic Load Balancer Load balancing as a service $0.025 per hour plus $0.008 per GB processed Works with EC2 autoscaling Supports SSL termination Can load balance between Availability Zones within a Region Can t load balance between regions. Rely on Route 53 DNS for region failover.
42 Horizontal Scaling We will use the same testing script from before Going to the homepage Waiting for up to 2 seconds Requesting a form to create a new community Waiting for up to 2 seconds Submitting the new community Requesting a form to create a new link submission Waiting for up to 2 seconds Submitting the new link Waiting for up to 2 seconds Delete the link Waiting for up to 2 seconds Delete the community
43 Horizontal Scaling When we test we will have 12 phases, of 60 seconds each: Phase Users/sec Remember these are users, not requests. There will be many requests per user, and users stay for 5-10s. Deployed using nginx & passenger.
44 Horizontal Scaling First we will look at breaking our database away from our single instance. This isn t horizontal scaling yet, but this change enables us to scale up the number of app servers
45 Horizontal Scaling 1 M3 Large Instance App server 2 vcpus 7.5 GB Memory SSD storage DB is also M3 Large. Responds well with 10 new users per second, but fails with 16 ~$200 a month
46 Horizontal Scaling Let s horizontally scale our app server by adding a second app server instance and see the effect on system performance
47 Horizontal Scaling 2 M3 Large Instance App server 2 vcpus 7.5 GB Memory SSD storage DB is also M3 Large. Responds well with 20 new users per second, but fails with 25 ~$300 a month
48 Horizontal Scaling Let s see how the system performs if we scale out to 5 app servers. Total dollar cost will be comparable to the most expensive single instance we tested
49 Horizontal Scaling 2 M3 Large Instance App server 2 vcpus 7.5 GB Memory SSD storage DB is also M3 Large. Responds well with 35 new users per second, does okay with 45, fails with 55 ~$600 a month
50 Horizontal Scaling Vertical scaling handled 20 new users per second for ~$600 per month, and left us with a nonexistent scaling path. Horizontal scaling handled 45 new users per second for ~$600 per month and left us with a clear path to increase scale
51 Motivation After today s lecture you should understand what load balancing is, and and why the architecture depicted here allows cost effective and smooth scaling paths.
52 For Next Time... me your group. Required info: Team name Each person s name, , github acct. Read/do chapters 9 through 17 in AWDR by next Tuesday. Lab is tomorrow, I will meet with each group to discuss projects. If you need technical help, come to Franz 1260 Friday s noon to 2pm.
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