The appender configuration section is what manages the log file. I've added comments to the appender for puppetserver.log, concerning what the individual lines are doing:

<!-- Setting the name for future reference and making a Rolling Log File -->
    <appender name="F1" class="ch.qos.logback.core.rolling.RollingFileAppender">

<!-- Logging to /var/log/puppetlabs/puppetserver/puppetserver.log -->
        <file>/var/log/puppetlabs/puppetserver/puppetserver.log</file>

<!-- Appending to, not replacing the log -->
        <append>true</append>

<!-- Roll the file over based on Size and Time -->
        <rollingPolicy class="ch.qos.logback.core.rolling.SizeAndTimeBasedRollingPolicy">

<!-- What to name the file as it's rolled over, with date variables -->
            <fileNamePattern>/var/log/puppetlabs/puppetserver/puppetserver-%d{yyyy-MM-dd}.%i.log.gz</fileNamePattern>

<!-- Maximum size of log file before rolling over -->
            <maxFileSize>200MB</maxFileSize>

<!-- Maximum Number of Files to keep - 90 logs -->
            <maxHistory>90</maxHistory>

<!-- Maximum Filesize of all files that will be kept. Up to 5 files with 200 MB -->
            <totalSizeCap>1GB</totalSizeCap>
        </rollingPolicy>
<!-- What to print for date and time with the message -->
        <encoder>
            <pattern>%d{yyyy-MM-dd'T'HH:mm:ss.SSSXXX} %-5p [%t] [%c{2}] %m%n</pattern>
        </encoder>
    </appender>

In the preceding example, we're creating puppetserver.log with a rollover strategy. We'll keep up to 90 logs, but we'll rotate whenever a log reaches 200 MB in size, and we will delete logs if we have more than 1 GB of logs. We'll append the date to logs that we roll over, and we will print the timestamp from the log.