Tag Archives: IP address

Migrating servers using DNS TTL for minimum downtime

You have your site running on an old hardware and want to migrate it to a new upgraded hardware which would result in change of the ipaddress of your site and in turn imply downtime for your site. You want to minimize the downtime due to the change in ipaddress. This can be easily achieved using the Time-to-live (TTL) values of the Domain Naming Service (DNS) entries of your website.

The users usually use your site name and not the ipaddress to visit to your site. DNS is used to resolve the site name to the correct ipaddress. The DNS entry is stored at various levels (browser, OS, proxy server, DNS servers, etc) and is cached for a specific period called as Time-to-live (TTL). Once the TTL expires, the DNS record will be fetched again from the DNS Server. Usually the TTL for a DNS entry is specified as 3600 sec (i.e. 1 hr). The TTL values can be even lower (0, i.e. no caching) or higher (up to 68 years).

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Getting real client IP address in PHP

Many times we need the visitor’s ipaddress for validation, security, spam prevention, etc. Getting the Visitor’s ipaddress is very easy in PHP.

The simplest way to get the visitor’s/client’s ipaddress is using the $_SERVER['REMOTE_ADDR'] or $_SERVER['REMOTE_HOST'] variables. The variable in the $_SERVER array are created by the web server (like apache) and we can use them in PHP.

// Get the client ip address
$ipaddress = $_SERVER['REMOTE_ADDR']

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