4. Detailed architecture
●
2 main processes
–
Parent is management
–
Child is actual caching process
●
●
●
●
●
●
Workers (one for each connection)
Thread pool manager (2 is default)
Startup thread
Health check
Acceptor
Reaper
4
5. Getting started
●
●
●
After installing varnish it will take the default
port of 6081 instead of 8080 as mentioned in
the manual.
Magic → /etc/sysconfig/varnish
(/etc/default/varnish for Debian)
Backend config : /etc/varnish/default.vcl
5
7. Cache storage
●
Hash
–
–
The options can be changed
–
●
HTTP Host header and the URL
Multiple objects can be mapped to the same key
Default backend in CentOS 6 is 'file'.
7
8. Storage backends
●
File
–
–
Not persistent across restart
–
●
Single file
Mmap
Malloc
–
–
●
It does a direct malloc()
Overhead 1kB per object
Persistent
–
Experimental (no disk space = fail!)
8
9. The basic tools of the trade
●
varnishd – The actual binary
●
varnishstat – Display stats
●
varnishlog – Display logs
●
varnishtop – Display most used log entries
–
varnishtop -i RxURL
●
varnishadm – Send command to varnishd
●
varnishncsa – Display apache/NCSA style logs
●
varnishhist – Histogram display
9
10. Logging in varnish
●
Done in shared memory
●
Overwrites once memory is full
●
No physical logs
●
Formats available are:
–
Apache format (NCSA)
–
Custom
–
Real-time
10
11. The log format
●
First column is
request ID
●
Second is tag
●
Third
c for client
b for backend
- for misc.
Then data.
11
12. The varnishstat utility
●
First column: Total of the type
●
Second: Total per second data
●
Third: Average rate since beginning of collection
12
13. Some Parameters from CLI
●
Thread pools (thread_pools)
●
Minimum no. of threads (thread_pool_min)
●
Maximum no. of threads (thread_pool_max)
●
No. of queued work requests (n_wrk_queued)
●
Timeout for idle and extra threads (thread_pool_timeout)
●
Wait time if new thread creation failed (thread_pool_fail_delay)
●
Timeout waiting for server's response (first_byte_timeout)
●
Network latency (connect_timeout)
●
Number of deleted cache entries (n_lru_nuked)
13
14. Changing startup options
●
Add the options as command line parameters in the
config file.
DAEMON_OPTS="-a :80
-T localhost:6082
-f /etc/varnish/default.vcl
-S /etc/varnish/secret
-s malloc,256m
-p first_byte_timeout=1s”
●
Edit the default vcl file and add the options as:
backend www {
.host = "127.0.0.1";
.port = "8080";
.first_byte_timeout = 1s;
...
}
14
16. How is it done?
●
The vcl is converted to C code
●
Code compile variable:
–
●
●
varnishadm param.show cc_command
The “.so” created is loaded with dlopen
The shared libraries can be found at :
/var/lib/varnish/$(hostname)/
16
18. Sailing in the vcl
●
vcl_recv()
–
–
●
When request is recv-d!
Data → req
vcl_fetch()
–
When response has been fetched.
–
Data → req and beresp
–
Try alternate backends, trigger ESI
18
19. What to do?
●
pass – No caching done
●
hit_for_pass – Cache decision to pass
●
lookup – Must deliver from cache
●
pipe – Varnish goes blind
●
deliver – Deliver cached object
19
20. VCL is C
●
In-line C code.
–
C{
}C
●
Prints to syslog
printf ( “Hey Jude!n” );
The compiled code:
–
varnishd -d -f foo.vcl -C
20
28. Grace
●
It can serve stale cache data via grace period
●
When it does that?
–
Too many connections pile up
–
A back-end is down
●
Detect by probes
backend server1 {
.host = "server1.example.com";
.probe = {
.url = "/";
.interval = 5s;
.timeout = 1 s;
.window = 5;
.threshold = 3;
}
}
●
Set both “beresp” grace and “req” grace for serving stale
data.
28
29. VMOD
●
●
Used to extend the functionality of basic inline
C allowed in a vcl.
vmod.cc
–
●
Generated file to be included with custom source
Custom locking for shared resources
29
