High availability tips & ideas

[Dimitris Tasoulis]

On Wed, 19 Feb 2003, Σταμάτης Κεκές wrote:

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> >
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> >Wpa, miso giati den dieukrinisthke kati e3arxhs:
> >
> >Egw auto pou katalaba einai pws o Stamaths exei:
> >
> >
> >                                 switch
> >
> >                  Load-balancer-1      Load-alancer-2
> >                     (active)            (standby)
> >
> >
> >        ftp-server-1    ftp-server-2   ftp-server-2   ftp-server-N
> >
> >
> >Opote skotwneis ton active kai kanei takeover o standby.
> >
> Nai Giorgo. To exo dokimasei ki ayto me LVS.
> 
> >
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> >To ftp server farm apo pisw einai zwntano sto sunolo.
> >
> >Ta katalaba swsta?
> >
> >An auto pou ennoouse o Stamaths pws psofaei einai enas ftp server, sumfwnw,
> >den mporei na metafernei to connection se kapoio allo ftp server.
> >
> >Filika.
> >
> Ego omos elega to eksis sxima
> 
> 
>                             switch
> 
>   Cluster Leaf 1 ( active )      Cluster Leaf 2 ( standby )
> 
>     Cluster proc
> 
>       ftpd
>       httpd
>       ....
> 
> Apla apo oso katalava symfona me ta osa diavasa kai sto site tis M$
> einai oti pernaei oxi mono ta sockets alla kai ta processes.
> Pragma pou me ton tropo pou anaferomaste edo den mporei na isxysei
> logo tou oti kai to lvs alla kai to heartbeat to mono pou kanoun einai
> an doune oti kapoios host einai kato to men heartbeat kanei IP address
> takeover kai meta ksekinaei ena ena ta initscripts pou tha tou pei
> kaneis sto /etc/ha.d/haresources eno to LVS xrisimopoiei to heartbeat
> gia na krataei zontano ton director pou me ti seira tou opos parethese
> poly sosta o Giorgos to sxima, kanei dromologisi ton connections pro tous
> real servers.
>  Ayto pou nomizo oti kalyptei ayto pou ithela apo tin arxei apo oso diavasa
> kai simera einai to beowulf. Pou stin ousia yparxei ena master node pou
> kanei resource management kai oi compute nodes. Den ksero omos mai pou den
> prolava na diavaso epi tou thematos an yparxei i dynatotita na yparxei kai
> deytero master node.
>  Etsi ola ta compute nodes ginontai ena virtual computer no matter who dies
> oti pliroforia xreiazetai gia kapoio process pernaei stous kernels ton 
> compute
> nodes kai etsi kseroun ta processes to state tous ktl ktl.
> 

To beowulf ka8os kai to mosix einai tetoiou eidous sximata, sta opoia
iparxei ena server pool kai ena node pool.

Sto server pool mporoun na iparxoun parapano apo 1 mixanima opos kai sto 
node pool. I diafora einai oti oi server prepei na einai afosoiomenoi sto 
cluster kai na diaxeirizontai ton ap8ikeytiko xoro pou mporei na einai 
distributed  alla mporei kai na min einai.

Ta nodes mporoun na eiserxontai sto cluster opotedipote 8elisoun na 
ekteloun ena komatti ipologismou kai meta an to 8elisoun na figoun 3ana.

Ayti einai genika i filosofia tou ka8e clustering perivalontos apo oso exo 
diavasei. Xrisimopoiountai poli  kai me stoxo to high availability ka8os i 
anixneysi an ena mixanima exi provlima ginetai aytomata alla kai me stoxo
to high performance opos eiani aytonoito. 



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