Azure Autoscale Restarts Running Instances

问题

I've been using Autoscale to shift between 2 and 1 instances of a cloud service in a bid to reduce costs. This mostly works except that from time to time (not sure what the pattern seems to be here), the act of scaling up (1->2) causes both instances to recycle, generating a service outage for users.

Assuming nothing fancy is going on in RoleEntry in response to topology changes, why would scaling from 1->2 restart the already running instance?

Additional notes:

It's clear both instances are recycling by looking at the Instances tab in Management Portal. Outage can also be confirmed by hitting the public site.
It doesn't happen consistently but I'm not sure what the pattern is. It feels like when the 1-instance configuration has been running for multiple days, attempts to scale up recycle both. But if the 1-instance configuration has only been running for a few hours, you can scale up and down without outages.
The first instance always comes back much faster than the 2nd instance being introduced.

回答1:

This has always been this way. When you have 1 server running and you go to 2+, the initial server is restarted. In order to have a full SLA, you need to have 2+ servers at all time.

回答2:

Nariman, see my comment on Brent's post for some information about what is happening. You should be able to resolve this with the following code:

public class WebRole : RoleEntryPoint
{
    public override bool OnStart()
    {
        // For information on handling configuration changes
        // see the MSDN topic at http://go.microsoft.com/fwlink/?LinkId=166357.
        IPHostEntry ipEntry = Dns.GetHostEntry(Dns.GetHostName());
        string ip = null;
        foreach (IPAddress ipaddress in ipEntry.AddressList)
        {
            if (ipaddress.AddressFamily.ToString() == "InterNetwork")
            {
                ip = ipaddress.ToString();
            }
        }

        string urlToPing = "http://" + ip;
        HttpWebRequest req = HttpWebRequest.Create(urlToPing) as HttpWebRequest;
        WebResponse resp = req.GetResponse();
        return base.OnStart();
    }
}

回答3:

You should be able to control this behavior. In the roleEntrypoint, there's an event you can trap for, RoleEnvironmentChanging.

A shell of some code to put into your solution will look like...

RoleEnvironment.Changing += RoleEnvironmentChanging;

private void RoleEnvironmentChanging(object sender, RoleEnvironmentChangingEventArgs e)
{
}

RoleEnvironment.Changed += RoleEnvironmentChanged;

private void RoleEnvironmentChanged(object sender, RoleEnvironmentChangedEventArgs e)
{
}

Then, inside the RoleEnvironmentChanged method, we can detect what the change is and tell Azure if we want to restart or not.

if ((e.Changes.Any(change => change is RoleEnvironmentConfigurationSettingChange)))
{
    e.Cancel = true; // don't recycle the role
}

来源：https://stackoverflow.com/questions/22252802/azure-autoscale-restarts-running-instances

标签

azure

azure-role-environment