Your website is down or not available. What you going to do?
Do not panic
Usually, it is one of three major reasons. Lots of minor reasons.
You may be able to reboot (switch off – pause 5 seconds – switch on) your router often to good effect. Certain versions of Windows and certain hardware may require you to restart them when they get too confused. Same thing can happen to anything, of course. With Mac, it should just work so if it don’t something is wrong.
Check no cables have become unconnected and inspect modem lights, etc.
You may have to clear your DNS Cache – restart your browser – restart your computer (rarely is that the case with Web apps) – restart your life (buy a new computer – not necessary but sometimes it is a good move).
if normal actions do not resolve the issue then,
There are several reasons.
The thing to focus upon is what everyone else sees.
It is tragically (for the beginner webmaster) quite easy to become convinced that everything is working when the rest of the web is not seeing your website. It is also quite amusing to watch an expert getting frustrated that a website appears unavailable when you can verify that it actually is running without a problem.
It is one of those things experts may not admit to, but testing is usually the last thing they consider necessary in the process of development.
The reason for that is you may need to clear the local DNS cache.
The DNS is a latent distributed database. It looks at the most available record in a chain of connected sources for an A record that reveals the endpoint address (IP address). The it can send a message to your browser saying “look here:” with the address. The address that gets returned to you is the most available one. There are other ones that may or may not have been subject to a DNS cache update.
Time to live
When we do a DNS query, it returns the TTL which is the number of seconds left that this name will be cached before this DNS leaf refreshes from the latest information from the parent branch. That the parent branch already have the latest information is dependent upon their parents, and so forth. An efficiently cached DNS system is a fast internet.
If suddenly all resources had very low TTLs the entire system would become hyperactive and fail. If a number adjust their TTLs it would not affect the overall latency that makes the internet work well. A hyperactive TTL only increases load between one host and its parent node.
I think I understand this
When we get to the leaf node level, the TTL needs to be higher than the parent for the distributed refresh mechanism to work efficiently. I define efficiently to mean that the most likely latest refresh be the intended setting from the latest update in pretty much the same time period, say synchronised within one day is certainly acceptable.
Setting the TTL low can help to change resource addresses more quickly but latency is the oil that makes the DNS work properly so when a domain switches it progressively does so everywhere. I am not a DNS programmer and am not suggesting that is the actual thinking behind their algorithm but it makes sense that everyone’s next query should return the new domain simultaneously and this is most likely if TTLs are at least the same or progressively larger as you step down the node tree.
Do not mess with your domain. Create new website versions under a subdomain. Do it openly or behind a password.
Reducing the TTL settings on Domains does not speed up your website. It is there for a good reason.
If a DNS setting works, don’t change it unless you absolutely know what you are doing. For new ideas use subdomains.
It may not work the way you expect it to, can disconnect your website for days without you knowing why (or appear to do that).