Linux System Administration 2 - HTTP, Apache, Nginx

1. WEB?
HTTPHTTP
ApacheApache
NginxNginx

2. HTTP
● Text based protocl defined in 1991
● V0.9 defined default port 80
● uses TCP/IP connection but should be able to run
on any connection oriented protocol
● RFCs 2616, 5785, 6266, 6585, 3986, 6874

3. HTTP vs. Gopher
● HTTP defines HTML as formatting for documents
● Gopher defines menu style format
● HTTP does not define any easy for searching and
indexing pages
● Trough its simple structure, gopher allows easy
search and indexing
● HTTP 80rfc2616 Gopher 70rfc1436
● Gopher defined the URI standard

4. HTTP
– Methods
– Requests
– Responses
– Headers
– URI/URL
– CGI

5. HTTP Methods
Method URI Proto
GET /lib/ana/sex.txt HTTP/1.0
● GET
● HEAD
● POST
● OPTIONS
● TRACE
● PUT
● DELETE

6. HTTP Requests
Method URI Proto + CRLF
HEADER + CRLF
HEADER + CRLF
CRLF
GET /pics/ana/naked.jpg HTTP/1.0 + CRLF
Range: 2400-2600,2900-3200 + CRLF
CRLF

7. HTTP Responses
GET /pics/ana/naked.jpg HTTP/1.0 + CRLF
Range: 2400-2600,2900-3200 + CRLF
CRLF
Proto Status Reason
HTTP/1.0 200 OK + CRLF
Response headers + CRLF
CRLF
.... binary data here .....

8. HTTP proto differences
● HTTP/1.0
– close connection after each request
● HTTP/1.1
– Host header
– Connection: keep-alive
– CONNECT method

9. Uniform Resource Identifier
(URI)
● UR Locator - URL
● Protocols: file, http, https, ftp, ftps, mailto, telnet,
ssh, smb, irc
proto :// user:pass @ host : port / path ? params
params:
param=value & param=value

10. Common Gateway Interface
(CGI)
● CGI is not Computer Generated Imagery :)
Web Server
Dynamic Content Generator
(CGI script)
SERVER_SOFTWARE
SERVER_NAME
GATEWAY_INTERFACESERVER_PROTOCOL
SERVER_PORT
REQUEST_METHOD
PATH_INFO - request path
PATH_TRANSLATED - full fs path
SCRIPT_NAME - request path
QUERY_STRING
REMOTE_HOST
REMOTE_ADDR
AUTH_TYPE
REMOTE_USER
REMOTE_IDENT
CONTENT_TYPE
CONTENT_LENGTH

11. Common Gateway Interface
(CGI)
● CGI is not Computer Generated Imagery :)
Web Server
Dynamic Content Generator
(CGI script)
/bin/sh + special
environment variables
1. Create a new environment
2. Create a new shell process
3. Execute the script
Note: the script must be executable and must
be able to produce the required output.
Responses must start with:
Content-type: some-type + CRLF
Responses may include Status codes:
200 OK + CRLF

12. Apache
● Documentation
● Module architecture
● Multi-processing Modules (MPMs)
● Additional Modules

13. MPMs - Prefork
● mpm_common
● Prefork
● Worker
● Event
Child
Child
Child
Memory
Memory
Memory
Memory
Main
Process

14. MPMs - Worker
● mpm_common
● Prefork
● Worker
● Event
Child
Child
Child
Main Process
Memory

15. MPMs - event
● mpm_common
● Prefork
● Worker
● Event
desc_ready = select(1, &rfds, NULL, NULL, &tv);
for (i=0; i <= max_fd && desc_ready > 0; ++i) {
VS.
for (;;) {
nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);

16. Module structure - Startup
● Pre-Config
● Test Configuration
● Post Configuration
● Open Logs
● Child Init
– Note that all of these are performed at least two times!

17. Module structure - Request
● Pre-Connection
● Create Connection
● Process Connection
● Create Request
● Post-Read Request
● Header Parse
● HTTP Scheme
● Default Port
● Quick Handler
● Translate Name
● Map to Storage
● Check Access
● Verify User ID
● Verify User Access
● Check Type
● Fixups
● Insert Filters
● Content Handlers
● Logging
● Insert Errors

18. Apache - Content handlers
module_name module_file mime_type priority
cgi_module mod_cgi.c .cgi .pl .sh 10
php_module mod_php.c .php .php5 10
perl_module mod_perl.c .pl .pm 10

19. Apache - CGI execution
Apache
Child mod_php
Child mod_cgi
root
nobody
nobody
Child mod_cgi
Child mod_suphp
index.php
index.php
suexec
index.php
/bin/sh
/bin/sh
suphp
index.php/bin/sh
user
user

20. Apache - CGI execution
Apache
Child mod_fcgid
Child mod_fcgid
root
nobody
user
index.php
FastCGI
daemon
child
child
child
index.php
index.php
suexec

21. Apache structure
● bin/
– httpd - the server
– ab - Apache Bench
– apxs - externel module builder
– htpasswd
– suexec
● conf/
– httpd.conf
– mime.typs + magic
● modules/ (libexec on 1.3)
● logs/