Integrated Cache on Netscaler

Integrated Cache Training –
Netscaler Webinar

Mark Hillick

Agenda of Cash, sorry Cache
•  Goals of Caching

q Why & What

•  Cache Policies

•  How long to cache

•  Memory for Cache

•  IC configuration
example

•  Cache Statistics

•  Troubleshooting IC
© 2007 Citrix Systems, Inc. — All rights reserved 2

Presentation Goal

Please be aware that this a technical presentation with lots of detail
and it is intended that it can be used as a reference guide at a later
date (e.g. when you're on-site).

Sadly, it s not like my usual Zen presentation with lots of funny
pictures and jokes, sorry L


Caching Goals

•  Caching would be useless if it did not significantly improve
performance.

•  Goal => to eliminate the need to send requests in many cases.

q Reduces the number of network round-trips required for many
operations - we use an "expiration" mechanism for this
purpose

•  Goal => remove the need to send full responses in many other
cases.

q  The latter reduces network bandwidth requirements - we use
a "validation" mechanism for this purpose

Caching is Used Everywhere

•  Local cache in your browser

•  Cache in the office (Forward Proxy or Transparent)

•  Cache at the ISP (Transparent)

•  Cache at the origin (Reverse Proxy or Transparent)

•  Cache integrated inside a traffic manager – much better J


Caching Benefits.

1.  Saves Bandwidth

2.  Reduces traffic to back-end server & so saves processing
resources

3.  Protects back-end servers from flash crowds

4.  Improves the response time & Increases site capacity

P.S. Even more benefits when integrated within a LB J


IC in Packet-Processing
TCP Processing

SSL Decrypt

HTTP Parsing

AAA Processing

Cache Redirection

Content Switching

Application Firewall

Responder Action?

Cache Hit?

HTTP Cache Req Policies

Rewrite Policy Eval

Load Balancing

Content Filtering


Non-Caching Proxy

GET /foo/index.html HTTP/1.1 GET /foo/index.html HTTP/1.1
Host: www.example.com Host: www.example.com

Proxy

HTTP/1.1 200 OK HTTP/1.1 200 OK
Last-Modified: Thu, ... Last-Modified: Thu, ...
Content-Length: 3688 Content-Length: 3688
Content-Type: text/html Content-Type: text/html


Caching Proxy: Miss


Proxy

HTTP/1.1 200 OK HTTP/1.1 200 OK
Last-Modified: Thu, ... Last-Modified: Thu, ...
Content-Length: 3688 Content-Length: 3688
Content-Type: text/html Content-Type: text/html

Proxy Cache
(Saves copy)


Caching Proxy: Hit

GET /foo/index.html HTTP/1.1
Host: www.example.com

Proxy

HTTP/1.1 200 OK
Last-Modified: Thu, ...
Content-Length: 3688
Content-Type: text/html

Proxy Cache
(Fresh copy!)


HTTP Response after a hit
•  wget -S --header="If-None-Match:23834-b1-4951a45768b8d" -U
Mozilla http://10.90.196.68/index.html

•  HTTP/1.1 200 OK
………

•  Via: NS-CACHE-9.2: 65
•  ETag: "23834-b1-4951a45768b8d"
•  Server: Apache/2.2.14 (Ubuntu)
......... OR .........

•  ETag: "23834-b1-4951a45768b8d"
•  2011-04-26 18:22:56 ERROR 304: Not Modified.
………


HTTP Response after a miss

•  $ wget -S --header="If-None-Match:23834-b1-4951a45768b8d" -U
Mozilla http://10.90.196.68/index.html
……….
•  HTTP/1.1 200 OK
•  Date: Wed, 27 Apr 2011 09:30:59 GMT
•  Server: Apache/2.2.14 (Ubuntu)
•  Last-Modified: Mon, 15 Nov 2010 16:52:53 GMT
………..
•  Saving to: `index.html.41


What Not to Cache

•  Cache-Control: no-store =>applies to entire message (req/resp)
•  Cache-Control: no-cache =>server cannot respond with cached
response
•  Cache-Control: Private => not by shared cache
q More info see -
http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html
•  POST request.
•  Don t cache if set-cookie exists
•  Don t cache all 5xx response codes, example 503 (Gateway time out)

•  By default, NS ignores cache-control headers in requests -> CG
Settings

Freshness

•  Describes how long the associated representation is fresh for.

q No need to send a request to server if object has not expired

q Saves time

•  Expires: Fri, 30 Oct 1998 14:19:41 GMT

•  Cache-Control: max-age=3600


Validation

•  Validation – once expired, validator can be used to check with the
server if the object is still valid.

q  Send conditional request and get a short “304 Not Modified”
response
q  Saves bandwidth

•  If-Modified-Since <Date>

•  If-None-Match <Etag>


Caching Proxy: Validation

If-Modified-Since: Thu, ...
Proxy

HTTP/1.1 200 OK HTTP/1.1 304 Not Modified
Last-Modified: Thu, ... Date: Fri, ...
Content-Length: 3688
Content-Type: text/html

Proxy Cache
(Saves copy)


Cacheability Policies
•  Specifies if response is cacheable.
q  Request or Response-based policy
•  CG is DEFAULT by default J but can be changed.
•  Action types
q  CACHE: Transaction is cacheable. Store the object
q  NOCACHE: Transaction is non-cacheable.
q  MAY_NOCACHE
o  For request based policies only
o  The response may be cacheable. The default if no response
cacheability policy matches is to not cache the response.
q  MAY_CACHE
o  For request based policies only
o  The response may be cacheable. The default if no response
cacheability policy matches is to cache the response.
q  INVAL
o  Mark the object as invalid

Cache Decision Time

•  Cache, Nocache, Inval
q  Cache decision @ request time & unless something that prevents decision
like CL mistmatch, no policy eval @ response time

•  MAY_CACHE, MAY_NOCACHE
q  Cache decision @ response time


Invalidate versus Expire

•  Invalidate
q  Invalidate will invalidate the object/"all objects in contentgroup".
q  But the way it is done is it is optimized such a way that we don't look at
each object and remove it but when you run expire command or when new
request comes for the invalid object, it is then removed.

q  We serve a full response (200) to client regardless of cache hit.

•  Expire
q  Only mark the object as expired
q  Request comes in & instead of getting full response (i.e what we do for
invalid object) we will send if-modified-since/if-none-match conditional
request to back-end server. i.e can receive a 304.


Content Group
•  Every cached object => member of CG
q  No CG, object => Default
q  minhit – no. of hits before store
•  Properties of objects can be controlled per contentgroup
•  Dynamic versus Static - parametised
•  Configurations per content-group are
q  Expiry settings
q  Portions of object considered for caching as well as Invalidation
[Parameterized Caching]
q  Pre-fetch objects before it gets expired (event-driven)
q  Inserting headers (e.g. Via header)
q  Memory related configuration for the objects and for this whole groups


Flash Cache (FC)
•  FC
q Improves performance –> 1 req to back-end server
q Concurrent requests queued on NS & single response served
q set/add cache contentgroup <group_name> -flashCache YES

q POWERFUL

q Cannot enable with PET (ensures IC polls origin before serving)


Some Other CG settings
•  Expiry settings (blank by default)
q Relexpiry – relative -> overrides server response settings
q heurexpiryParam - %
q Expire after complete response received
•  If no expiry settings & none in response => cache miss but can do
validation (non-fc)

•  Cache controls
q No cache depending on size or hits
q Mem limit usage per group
•  Works with FC J but probably not wise on significant groupsExpire
after complete response received


Cache Policies

•  Built-In (begin with “__” & “ctx_”)
q Greatly enhanced in 9.3 – should be sufficient for most

•  Bound globally or per vServer
q Easy-To-Administer & View within Global Policy Manager

•  PI-based expression engine like other NS features


Cache

•  Built-In (begin with “__” )
q Greatly enhanced in 9.3 – should be sufficient for most

•  Bound globally or per vServer
q Easy-To-Administer & View within Global Policy Manager

•  PI-based expression engine like other NS features


Verification

•  Three Verification Options (again sh cache pa)

q Hostname (Sufficient for Most Companies)

q Hostname & IP (Default)

q DNS (Most Secure)


Flushing the Cache
•  Flush Cache
q Remove stale content manually
q Troubleshooting (preferred flush, disable, enable)
q CLI – either CG or Object
o  flush cache contentGroup content_group_html
o  flush cache contentGroup ALL
o  flush cache object –locator <0x….>
q GUI – IC > Cache Objects

•  Automatic CG flush once CG configuration is modified


Cache Memory Management (1)
•  BSD & PPE First
•  7500 with 8gb RAM & 3 PE
q 2gb for kernel, 3gb for PE & max 3gb for IC
q Each PE has minimum of 1gb

•  17500 – 48gb mem & 11 PE
q 2gb for kernel, 23gb to PE & IC can take up to 23gb
q Each PE cannot exceed 3.2gb address space

•  IC takes up what’s left (!>0.5)


Cache Memory Management (2)
•  > set cache pa –memLimit 254
•  > sh cache pa | grep -i mem
Memory usage limit: 10000 MBytes

Memory usage limit (active value): 10000 Mbytes => reboot

Maximum value for Memory usage limit: 15662 MBytes

•  > sh cache contentgroup
•  Memory Allocation Issues
q cli> stat cache –detail | grep alloc

Memory allocation failures 5741 => cache misses


Cache Selectors
•  Best practice to configure selectors (preferred over parameters)
•  Named filter – locates particular objects in CG, not exact match
•  Associate selector based on the request, not with responses
•  Sample selectors
•  http.req.url; http.req.method; client.ip.dst etc
•  Use cases
q One file only cached once regardless of hostname
q Two copies of same file – compressed & uncompressed
q Same file, same hostname but different VIPs & CGs


“Not Cache” Best Practice
•  Not Cache policies first
q Once IC is turned on, it will begin to cache as per the default
policies.

o  This may cause confidential content to be cached by
accidentThen cache known, good content

q Start with images – jpegs, gifs
q Check statistics for
o  Memory allocation errors
o  Hits
o  Misses
o  Expiries


Cache HTTP Callout
•  Callouts to external servers
q Cache saves multiple requests

•  add cache policy pol_callout -rule "CLIENT.IP.SRC.EQ
(127.128.129.130 )" -action CACHE –storeInGroup

•  bind cache global pol_callout –priority 100 –gotoPriorityExpression END
–type REQ_DEFAULT

•  sh cache object –locator <0x…>
HTTP callout cell: YES
HTTP callout name: callout1
HTTP callout type: TEXT
HTTP callout response: NO


Soft-Cache Expiry
•  When a back-end server does not respond quickly to requests, an
upstream NetScaler can serve responses from the cache.

q Liberal interpretation of RFC
q Protects back-end server further (e.g. lash-type event)
q Serves stale data for a minimal amount of time

•  Applies to 9.2.52.3 & above


Configuration through Wizard (1)
•  Easy-to-use J


Example Configuration
•  enable feature IC

•  set cache parameter –memlimit 512

•  add cache contentgroup cg_image –relExpiry 600 –memLimit 100 –
maxResSize 512

•  add cache policy cp1 –rule http.req.url.contains(“jpeg”) –action cache
–storeingroup cg_image

•  bind cache global cp1 –priority 1 –type REQ_DEFAULT

cli> sh cache object
0x000000078b4200000004 cg_image //10.102.30.16:80/abc.jpeg


Statistics via the CLI (1)

•  cli> sh cache object
0x000000078b4200000004 cg_image //10.102.30.16:80/abc.jpeg

•  cli> sh cache object –locator 0x000000078b4200000004
q  Address in Memory

•  nscachemgr –a/-g <contentgroup>
q  Shell Equivalent

•  Use grep – POWERFUL for parsing output for hits, misses etc.


Statistics via the CLI (2)


Statistics via the GUI (1)


Troubleshooting Tools1

•  Browser -> inconsistencies & can be very frustrating L
q FF (HTTP Fox & Tamper Data Extensions but FF4 issues)
q IE (7, 8, 9) -> Fiddler
q Opera & Chrome -> as standard, no extensions

•  Tracing & PCAP ->
q Nstrace & Wireshark as usual J


Troubleshooting Tools2

•  Paros (as a proxy in the middle) -> I now use Zap (Owasp project fork of
Paros)

•  CLI -> no user-cache to worry about J
q wget
•  wget –S –header=“If-None-Match:etag_value” http://test.com/file.jpg
q curl
o  curl –header “If-None-Match: etag_value” test.com/index.html


Troubleshooting

•  Cache turned on but no cache objects
q  sh cache pa != Memory usage limit: 0 bytes
q  Zero memory = cache misses
o  Warning msg in 9.2 when sh cache object
q  Check expiry settings? NS? Server?

•  Blank entries in nscachemgr output?
q  //10.90.196.76/
q  //10.90.196.76/citrix_logo.jpg
q  Default caching properties of GET / HTTP/1.1


CTX Articles (just a snapshot)

•  http://support.citrix.com/article/CTX124553 - how to IC
•  http://support.citrix.com/article/CTX123753 - compressed
content to unadvertised clients
•  http://support.citrix.com/article/CTX126557 - caching
uncompressed & compressed content of same file
•  http://support.citrix.com/article/CTX128801 - same
hostname/object but different vip twice
•  http://support.citrix.com/article/CTX129118 - has my HTTP
callout been cached
•  http://support.citrix.com/article/CTX124718 - cache callout
response
•  http://support.citrix.com/article/CTX129734 - Soft Cache
Expiry


Extra Reading

•  You can use perl, curl, wget, browser add-ons but I like wget –
q  http://www.cyberciti.biz/tips/linux-wget-your-ultimate-
command-line-downloader.html
q  http://www.computerhope.com/unix/wget.htm
q  Google “wget site:www.linuxquestions.org”
q  Easy to write a basic shell script around it & doesn’t need
to be too complicated

•  RFC 2616 (HTTP) VERY IMPORTANT
q  Section 13 (Caching)
q  Section 14 (Headers)


So with IC you can, take over….


Sláinte


Integrated Cache on Netscaler

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