Configure log4j for logstash using dockerfile

Elastic Stack Logstash
1

I recently started working on logstash. I am running it in docker and I want to read its logs using 'docker logs <container_name>' command. But I am getting error

log4j:WARN No appenders could be found for logger (org.apache.http.client.protocol.RequestAuthCache).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

My dockerfile is as below, please let me know how to configure log4j using dockerfile.

FROM debian:jessie
ENV DEBIAN_FRONTEND noninteractive
RUN echo "deb http://http.debian.net/debian jessie-backports main" >> /etc/apt/sources.list && \
    rm -rf /var/lib/apt/lists/* && \
    apt-get -y update && \
    apt-get -y upgrade && \
    apt-get -y --force-yes install sudo wget logrotate texinfo build-essential openjdk-7-jdk ant git zip && \
    apt-get autoclean && \
    apt-get autoremove && \
    rm -rf /var/lib/apt/lists/*

# Install logstash package
RUN wget --quiet https://download.elastic.co/logstash/logstash/packages/debian/logstash_2.3.0-1_all.deb && \
    dpkg -i ./logstash_2.3.0-1_all.deb && \
    rm ./logstash_2.3.0-1_all.deb


ENV PATH /opt/logstash/bin:$PATH
CMD ["/usr/bin/sudo", "-E", "-u", "logstash", "/opt/logstash/bin/logstash", "-f",  "/etc/logstash/logstash.conf"]
EXPOSE 5000-5100/tcp 5000-5100/udp

# Config ls
ENV LS_HEAP_SIZE 12288M
ADD logstash.conf /etc/logstash/logstash.conf

# Configuring log4j
ADD log4j.properties /etc/logstash/config/log4j.properties
2

What's in log4j.properties? What if you remove its ADD stanza from the dockerfile?

3

I tried removing ADD stanza but it did not work.
Contents of log4j.properties.

log4j.rootLogger=INFO, console, socketappender

PATTERN=[%d{ISO8601}][%-5p][%-25c] %m%n

log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern=${PATTERN}

Can you please let me know what is wrong with my configuration?
Thank you in advance!