High availability tips & ideas

[Σταμάτης Κεκές]

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>Wpa, miso giati den dieukrinisthke kati e3arxhs:
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>Egw auto pou katalaba einai pws o Stamaths exei:
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>                                 switch
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>                  Load-balancer-1      Load-alancer-2
>                     (active)            (standby)
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>        ftp-server-1    ftp-server-2   ftp-server-2   ftp-server-N
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>Opote skotwneis ton active kai kanei takeover o standby.
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Nai Giorgo. To exo dokimasei ki ayto me LVS.

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>To ftp server farm apo pisw einai zwntano sto sunolo.
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>Ta katalaba swsta?
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>An auto pou ennoouse o Stamaths pws psofaei einai enas ftp server, sumfwnw,
>den mporei na metafernei to connection se kapoio allo ftp server.
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>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.