logback has switched from Layouts to Encoders

[jsyrjala]

logback has replaced Layout interface with Encoder interface since logback 0.9.19 in appenders. Maybe cloudwatch-logback-appender should follow that convention?

https://logback.qos.ch/manual/encoders.html

[j256]

Sorry for the delay. I'll look into this when I next push a release.

[github4sanjay]

really need this