index format change daily to weekly

Question

I am currently sending my Log from Nlog to ElasticSearch. I am creating Index daily, and send Logs to that index. I want to create Index Weekly, so I want to change config file.

I do index creation in NLog configuration file. index = "logstash-${date:format=yyyy.MM.dd}"

My NLog Configuration part :

  <target xsi:type="ElasticSearch" 
    index = "logstash-${date:format=yyyy.MM.dd}"
    uri="http://localhost:9200" 
    includeAllProperties ="true">
   </target>

I found in some forums (https://github.com/logstash-plugins/logstash-output-elasticsearch/issues/541#issuecomment-270923437) changing weekly I should use like xxxx.ww. I tried to change config file like this : index = "logstash-${date:format=xxxx.ww}"

Unfortunately this is give me result logstash-xxxx.ww, I expected result logstash-2019.25

So how can I change daily to weekly?

Answer 1

${date} accepts the same formats as DateTime.ToString. Unfortunately there is no ww or weeknumber format with .NET (see Custom date and time format strings - .NET | Microsoft Docs)

The link on the forum is talking about Joda Time, which is a library for Java and not .NET.

You could solve this with a custom layout renderer in NLog. Getting the week number in .NET is a bit tricky, got this from Get the correct week number of a given date:

// This presumes that weeks start with Monday.
// Week 1 is the 1st week of the year with a Thursday in it.
public static int GetIso8601WeekOfYear(DateTime time)
{
    // Seriously cheat.  If its Monday, Tuesday or Wednesday, then it'll 
    // be the same week# as whatever Thursday, Friday or Saturday are,
    // and we always get those right
    DayOfWeek day = CultureInfo.InvariantCulture.Calendar.GetDayOfWeek(time);
    if (day >= DayOfWeek.Monday && day <= DayOfWeek.Wednesday)
    {
        time = time.AddDays(3);
    }

    // Return the week of our adjusted day
    return CultureInfo.InvariantCulture.Calendar.GetWeekOfYear(time, CalendarWeekRule.FirstFourDayWeek, DayOfWeek.Monday);
}

Creating a layout renderer which renders 2019.25 etc (see NLog docs - How to write a custom layout renderer)

using NLog.LayoutRenderers;
using NLog;
...

// register ${myDateTime}. Register a soon as possible (e.g main(), app_start etc)
LayoutRenderer.Register("myDateTime", logEventInfo => 
    logEventInfo.TimeStamp.Year +"." + GetIso8601WeekOfYear(logEventInfo.TimeStamp));

and now this should work:

index = "logstash-${myDateTime}"