High availability tips & ideas

[Georgatos Vaggelis]

OOOOOOOOOOOOOOOOOOPpppppppp!!!!!!!!!!!!!

paidia exoume pelagodromisei -- ews mple3ei ta UTP kalwdia mas --...

Allo to clustering allo to fail over, kati pou kanei katapliktika to HA.
To HA DEN einai clustering software apla sthn periptwsh pou skash kati
sthn mia mhxanh me ena arp spoofing klp 8a sikosei MIA (mono dyo mporoun
na symetexoun) allh gia na kanei thn doulia apo ekei kai pera. Sto
clustering apo thn allh yparxei enas DIRECTOR, dhladh enas software
agent pou se M$ perivalonta trexei sto ena apo ta dyo melh tou cluster.
Kanonika prepei na trexei (apodotikotero or8otero klp) se mia trhth
mhxanh opote exeis to sxhma ginetai ws e3is:

exeis ena director pou 3erei ti kanei o ka8e server (status, load I/O
wait klp) kai ta requests pou tou erxontai (stnh periptwsh mas ftp
downl) o client den 3erei POTE amesa (kai den ton endiaferei) me poion
server mhlaei afto stelnei ta request sto Virtual IP to opoio to krataei
o director kai synalasetai me afton, ara AN symbei kati KAKO se ena apo
tous x servers pou kanei serve to en logo request tote DIAFANWS gia to
XRHSTH, ante na dei ena mhkro drop sthn taxhthta an kai gia afto
yparxoun ta buffers, 8a kanei o director re-establish to conection me
ena allo server kai 8a synexisei.

gia perisotera peri clustering se afto to epipedo rikste mia matia sto
http://www.LinuxVirtualServer.org pou exei kai polly orea docs .