Re: How to configure for remote TCP/IP client conncections using MS Visual Basic OLE DB calls and PostgreSQL dll's?

Steve Crawford <scrawford@xxxxxxxxxxxxxxxxxxxx> · Wed, 09 Mar 2011 10:55:35 -0800



    On 03/09/2011 09:54 AM, John Edens wrote:
    
      
        ------------
        Using
            * should be fine unless you have multiple IP addresses and
            want the *server* to *listen* on only some of those
            addresses - say localhost if you were running web and db on
            the same machine and didn't want to listen to connections
            from the outside. This setting only determines where the
            server listens. 
        -------------
         
        Okay,
            done that - what is the difference between  listening on
            only some of those addresses and allowing only clients in a
            certain range to connect?
         
        
    They are completely different.

    
    Your server can have multiple IP addresses. In fact, it almost
    certainly has an IP assigned to your NIC and a localhost address.
    But you could have multiple NICs in the machine and/or multiple IP
    addresses assigned to each NIC. This is very common - especially for
    web servers hosting several sites on different addresses. The
    addresses can be on different networks, as well.

    
    Suppose your server has addresses 10.1.1.2, 10.1.1.3 and
    192.168.1.4. If listen_addresses is set to *, a client could connect
    to PostgreSQL by connecting to any of those addresses - i.e. the
    host in their connection string could be any of the addresses you
    listen on. If that is not what you want, you need to explicitly list
    the addresses you want PostgreSQL to use.

    
    Now that you are listening on one or more addresses, the pg_hba.conf
    determines who is allowed to connect. It is completely independent
    of where you listen. It could include all IP addresses, or one or
    more individual IPs or IP ranges. And the IP addresses allowed for
    clients do not need to overlap your listen_address or be on the same
    IP network.

    
    By way of example, you could have three independent instances of
    PostgreSQL running on your machine - perhaps one for dev, one for QA
    and one for deployment-staging. You could have dev listen only on
    .2, QA on .3 and deploy on .4. You could even have a 4th, say
    "sandbox", listening on all (though it would have to have a
    different port). And each one of those instances could have
    different pg_hba.conf settings to restrict client access as
    appropriate.

    
    Cheers,

    Steve