Updated Dockerfile to support python3

Dockerfile

@@ -1,5 +1,5 @@
-FROM alpine:latest as py-ea
-ARG ELASTALERT_VERSION=v0.2.0b2
+FROM python:3.6-alpine as py-ea
+ARG ELASTALERT_VERSION=v0.2.1
 ENV ELASTALERT_VERSION=${ELASTALERT_VERSION}
 # URL from which to download Elastalert.
 ARG ELASTALERT_URL=https://github.com/Yelp/elastalert/archive/$ELASTALERT_VERSION.zip
@@ -9,7 +9,7 @@ ENV ELASTALERT_HOME /opt/elastalert
 
 WORKDIR /opt
 
-RUN apk add --update --no-cache ca-certificates openssl-dev openssl python2-dev python2 py2-pip py2-yaml libffi-dev gcc musl-dev wget && \
+RUN apk add --update --no-cache ca-certificates openssl-dev openssl libffi-dev gcc musl-dev wget && \
 # Download and unpack Elastalert.
  wget -O elastalert.zip "${ELASTALERT_URL}" && \
  unzip elastalert.zip && \
@@ -25,15 +25,14 @@ RUN sed -i 's/jira>=1.0.10/jira>=1.0.10,<1.0.15/g' setup.py && \
  pip install -r requirements.txt
 
 FROM node:alpine
-LABEL maintainer="BitSensor <dev@bitsensor.io>"
+LABEL maintainer="Securely <developer@securely.ai>"
 # Set timezone for this container
 ENV TZ Etc/UTC
 
-RUN apk add --update --no-cache curl tzdata python2 make libmagic
+RUN apk add --update --no-cache curl tzdata python3=3.6.8-r2 make libmagic
 
-COPY --from=py-ea /usr/lib/python2.7/site-packages /usr/lib/python2.7/site-packages
+COPY --from=py-ea /usr/local/lib/python3.6/site-packages /usr/lib/python3.6/site-packages
 COPY --from=py-ea /opt/elastalert /opt/elastalert
-COPY --from=py-ea /usr/bin/elastalert* /usr/bin/
 
 WORKDIR /opt/elastalert-server
 COPY . /opt/elastalert-server
@@ -47,8 +46,9 @@ COPY elastalert_modules/ /opt/elastalert/elastalert_modules
 
 # Add default rules directory
 # Set permission as unpriviledged user (1000:1000), compatible with Kubernetes
-RUN mkdir -p /opt/elastalert/rules/ /opt/elastalert/server_data/tests/ \
- && chown -R node:node /opt
+RUN ln -s /usr/bin/python3 /usr/bin/python && \
+ mkdir -p /opt/elastalert/rules/ /opt/elastalert/server_data/tests/ && \
+ chown -R node:node /opt
 
 USER node