private IReadOnlyList <DnsResourceRecord> GetAnswers(string domain, DnsQuestionRecord question, string zoneName, uint appRecordTtl, string healthCheck)
{
HealthCheckStatus status = _healthMonitor.QueryStatus(domain, question.Type, healthCheck, true);
if (status is null)
{
if (question.Name.Equals(zoneName, StringComparison.OrdinalIgnoreCase)) //check for zone apex
{
return new DnsResourceRecord[] { new DnsResourceRecord(question.Name, DnsResourceRecordType.ANAME, DnsClass.IN, 30, new DnsANAMERecord(domain)) }
}
; //use ANAME
else
{
return new DnsResourceRecord[] { new DnsResourceRecord(question.Name, DnsResourceRecordType.CNAME, DnsClass.IN, 30, new DnsCNAMERecord(domain)) }
};
}
else if (status.IsHealthy)
{
if (question.Name.Equals(zoneName, StringComparison.OrdinalIgnoreCase)) //check for zone apex
{
return new DnsResourceRecord[] { new DnsResourceRecord(question.Name, DnsResourceRecordType.ANAME, DnsClass.IN, appRecordTtl, new DnsANAMERecord(domain)) }
}
; //use ANAME
else
{
return new DnsResourceRecord[] { new DnsResourceRecord(question.Name, DnsResourceRecordType.CNAME, DnsClass.IN, appRecordTtl, new DnsCNAMERecord(domain)) }
};
}
return(null);
}
private void GetStatusAnswers(dynamic jsonAddresses, bool primary, DnsQuestionRecord question, uint appRecordTtl, string healthCheck, List <DnsResourceRecord> answers)
{
if (jsonAddresses == null)
{
return;
}
foreach (dynamic jsonAddress in jsonAddresses)
{
IPAddress address = IPAddress.Parse(jsonAddress.Value);
HealthCheckStatus status = _healthMonitor.QueryStatus(address, healthCheck, false);
string text = "app=failover; addressType=" + (primary ? "primary" : "secondary") + "; address=" + address.ToString() + "; healthCheck=" + healthCheck;
if (status is null)
{
text += "; healthStatus=Unknown;";
}
else if (status.IsHealthy)
{
text += "; healthStatus=Healthy;";
}
else
{
text += "; healthStatus=Failed; failureReason=" + status.FailureReason + ";";
}
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.TXT, question.Class, appRecordTtl, new DnsTXTRecord(text)));
}
}
private void GetAnswers(dynamic jsonAddresses, DnsQuestionRecord question, uint appRecordTtl, string healthCheck, List <DnsResourceRecord> answers)
{
if (jsonAddresses == null)
{
return;
}
switch (question.Type)
{
case DnsResourceRecordType.A:
foreach (dynamic jsonAddress in jsonAddresses)
{
IPAddress address = IPAddress.Parse(jsonAddress.Value);
if (address.AddressFamily == AddressFamily.InterNetwork)
{
HealthCheckStatus status = _healthMonitor.QueryStatus(address, healthCheck, true);
if (status is null)
{
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.A, question.Class, 30, new DnsARecord(address)));
}
else if (status.IsHealthy)
{
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.A, question.Class, appRecordTtl, new DnsARecord(address)));
}
}
}
break;
case DnsResourceRecordType.AAAA:
foreach (dynamic jsonAddress in jsonAddresses)
{
IPAddress address = IPAddress.Parse(jsonAddress.Value);
if (address.AddressFamily == AddressFamily.InterNetworkV6)
{
HealthCheckStatus status = _healthMonitor.QueryStatus(address, healthCheck, true);
if (status is null)
{
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.AAAA, question.Class, 30, new DnsAAAARecord(address)));
}
else if (status.IsHealthy)
{
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.AAAA, question.Class, appRecordTtl, new DnsAAAARecord(address)));
}
}
}
break;
}
}
public Task SendAlertAsync(IPAddress address, string healthCheck, HealthCheckStatus healthCheckStatus)
{
if (!_enabled || (_mailFrom is null) || (_alertTo is null) || (_alertTo.Length == 0))
{
return(Task.CompletedTask);
}
MailMessage message = new MailMessage();
message.From = _mailFrom;
foreach (MailAddress alertTo in _alertTo)
{
message.To.Add(alertTo);
}
if (healthCheckStatus.IsHealthy)
{
message.Subject = "[Alert] Address [" + address.ToString() + "] Status Is Healthy";
message.Body = @"Hi,
The DNS Failover App was successfully able to perform a health check [" + healthCheck + "] on the address [" + address.ToString() + @"] and found that the address was healthy.
Alert time: " + healthCheckStatus.DateTime.ToLongDateString() + @"
Regards,
DNS Failover App
";
}
else
{
message.Subject = "[Alert] Address [" + address.ToString() + "] Status Is Failed";
message.Body = @"Hi,
The DNS Failover App was successfully able to perform a health check [" + healthCheck + "] on the address [" + address.ToString() + @"] and found that the address failed to respond.
The failure reason is: " + healthCheckStatus.FailureReason + @"
Alert time: " + healthCheckStatus.DateTime.ToLongDateString() + @"
Regards,
DNS Failover App
";
}
return(SendMailAsync(message));
}
private void GetStatusAnswers(string domain, bool primary, DnsQuestionRecord question, uint appRecordTtl, string healthCheck, List <DnsResourceRecord> answers)
{
{
HealthCheckStatus status = _healthMonitor.QueryStatus(domain, DnsResourceRecordType.A, healthCheck, false);
string text = "app=failover; cnameType=" + (primary ? "primary" : "secondary") + "; domain=" + domain + "; qType: A; healthCheck=" + healthCheck;
if (status is null)
{
text += "; healthStatus=Unknown;";
}
else if (status.IsHealthy)
{
text += "; healthStatus=Healthy;";
}
else
{
text += "; healthStatus=Failed; failureReason=" + status.FailureReason + ";";
}
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.TXT, question.Class, appRecordTtl, new DnsTXTRecord(text)));
}
{
HealthCheckStatus status = _healthMonitor.QueryStatus(domain, DnsResourceRecordType.AAAA, healthCheck, false);
string text = "app=failover; cnameType=" + (primary ? "primary" : "secondary") + "; domain=" + domain + "; qType: AAAA; healthCheck=" + healthCheck;
if (status is null)
{
text += "; healthStatus=Unknown;";
}
else if (status.IsHealthy)
{
text += "; healthStatus=Healthy;";
}
else
{
text += "; healthStatus=Failed; failureReason=" + status.FailureReason + ";";
}
answers.Add(new DnsResourceRecord(question.Name, DnsResourceRecordType.TXT, question.Class, appRecordTtl, new DnsTXTRecord(text)));
}
}
public Task CallAsync(IPAddress address, string healthCheck, HealthCheckStatus healthCheckStatus)
{
if (!_enabled)
{
return(Task.CompletedTask);
}
HttpContent content;
{
using (MemoryStream mS = new MemoryStream())
{
JsonTextWriter jsonWriter = new JsonTextWriter(new StreamWriter(mS));
jsonWriter.WriteStartObject();
jsonWriter.WritePropertyName("address");
jsonWriter.WriteValue(address.ToString());
jsonWriter.WritePropertyName("healthCheck");
jsonWriter.WriteValue(healthCheck);
jsonWriter.WritePropertyName("isHealthy");
jsonWriter.WriteValue(healthCheckStatus.IsHealthy);
jsonWriter.WritePropertyName("failureReason");
jsonWriter.WriteValue(healthCheckStatus.FailureReason);
jsonWriter.WritePropertyName("dateTime");
jsonWriter.WriteValue(healthCheckStatus.DateTime);
jsonWriter.WriteEndObject();
jsonWriter.Flush();
content = new ByteArrayContent(mS.ToArray());
content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
}
}
return(CallAsync(content));
}
public HealthMonitor(IDnsServer dnsServer, IPAddress address, HealthCheck healthCheck)
{
_dnsServer = dnsServer;
_address = address;
_healthCheck = healthCheck;
_healthCheckTimer = new Timer(async delegate(object state)
{
try
{
if (_healthCheck is null)
{
_healthCheckStatus = null;
}
else
{
HealthCheckStatus healthCheckStatus = await _healthCheck.IsHealthyAsync(_address);
bool sendAlert = false;
if (_healthCheckStatus is null)
{
if (!healthCheckStatus.IsHealthy)
{
sendAlert = true;
}
}
else
{
if (_healthCheckStatus.IsHealthy != healthCheckStatus.IsHealthy)
{
sendAlert = true;
}
else if (_healthCheckStatus.FailureReason != healthCheckStatus.FailureReason)
{
sendAlert = true;
}
}
if (sendAlert)
{
EmailAlert emailAlert = _healthCheck.EmailAlert;
if (emailAlert is not null)
{
_ = emailAlert.SendAlertAsync(_address, _healthCheck.Name, healthCheckStatus);
}
WebHook webHook = _healthCheck.WebHook;
if (webHook is not null)
{
_ = webHook.CallAsync(_address, _healthCheck.Name, healthCheckStatus);
}
}
_healthCheckStatus = healthCheckStatus;
}
}
catch (Exception ex)
{
_dnsServer.WriteLog(ex);
if (_healthCheckStatus is null)
{
EmailAlert emailAlert = _healthCheck.EmailAlert;
if (emailAlert is not null)
{
_ = emailAlert.SendAlertAsync(_address, _healthCheck.Name, ex);
}
WebHook webHook = _healthCheck.WebHook;
if (webHook is not null)
{
_ = webHook.CallAsync(_address, _healthCheck.Name, ex);
}
_healthCheckStatus = new HealthCheckStatus(false, ex.ToString());
}
else
{
_healthCheckStatus = null;
}
}
finally
{
if (!_disposed && (_healthCheck is not null))
{
_healthCheckTimer.Change(_healthCheck.Interval, Timeout.Infinite);
}
}
}, null, Timeout.Infinite, Timeout.Infinite);
_healthCheckTimer.Change(0, Timeout.Infinite);
}