Check if a server is available

Question

Hi,

I'm looking for a way to check if a server is still available. We have a offline application that saves data on the server, but if the serverconnection drops (it happens occasionally), we have to save the data to a local database instead of the online database. So we need a continues check to see if the server is still available.

We are using C# for this application

Greetz,

Sem

ps: the check on the sqlconnection.open is not really an option because this takes about 20 sec before an error is thrown, we can't wait this long + i'm using some http services as well.

Answer 1

Does this example code help you?

Answer 2

Just use the System.Net.NetworkInformation.Ping class. If you server does not respond to ping (for some reason you decided to block ICMP Echo request) you'll have to invent you own service for this. Personally, I'm all for not blocking ICMP Echo requests, and I think this is the way to go. The ping command has been used for ages to check reachability of hosts.

using System.Net.NetworkInformation;
var ping = new Ping();
var reply = ping.Send("google.com", 60 * 1000); // 1 minute time out (in ms)
// or...
reply = ping.Send(new IPAddress(new byte[]{127,0,0,1}), 3000);

Answer 3

Since you want to see if the database server is there either catch any errors when you attempt to connect to the database or use a socket and attempt a raw connection to the server on some service, I'd suggest the database as that is the resource you need.

Answer 4

If this is an sql server then you can just try to open a new connection to it. If the SqlConnection.Open method fails then you can check the error message to determine if the server is unavailable.

Answer 5

If the connection is as unreliable as you say, I would not use a seperate check, but make saving the data local part of the exception handling. I mean if the connection fails and throws an exception, you switch strategies and save the data locally.

If you check first and the connection drops afterwards (when you actually save data), then you still would still run into an exception you need to handle. So the initial check was unnecessary. The check would only be useful if you can assume that after a succesfull check the connection is up and stays up.

Answer 6

What you are doing now is:

• use distant server
• if distant server fails, resort to local cache

How to determine if the server is available? Use a catch block. That's the simplest to code.

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If you actually have a local database (and not, for example, a list of transactions or data waiting to be inserted), I would turn the design around:

• use the local database
• regularly synchronize the local database and the distant database

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I'll let you be the judge on concurrency constraints and other stuff related to your application to pick a solution.

Answer 7

From your question it appears the purpose of connecting to the server is to use its database. Your priority must be to check whether you can successfully connect to the database. It doesn't matter if you can PING the server or get an HTTP response (as suggested in other answers), your process will fail unless you successfully establish a connection to the database. You mention that checking a database connection takes too long, why don't you just change the Connection Timeout setting in your application's connection string to a more impatient value such as 5 seconds (Connection Timeout=5)?