Set the version number of the Python interpreter and its Elasticsearch client module

Dockerfile

-FROM python:slim
+FROM python:3.7-slim
 
 # cf. https://github.com/nodesource/distributions/blob/master/README.md#installation-instructions
 RUN apt update && apt install -y curl gnupg
-RUN curl -sL https://deb.nodesource.com/setup_11.x | bash -
+RUN curl -sL https://deb.nodesource.com/setup_12.x | bash -
 RUN apt install -y nodejs
 
 WORKDIR /app
@@ -10,15 +10,15 @@ COPY requirements.txt .
 COPY package.json .
 COPY package-lock.json .
 
+RUN pip install -r requirements.txt
+RUN npm install
+
 COPY lib/*.py ./lib/
 COPY lib/jwt_factory.js ./lib/
 COPY templates/*.html ./templates/
 COPY api.py .
 COPY main.py .
 
-RUN pip install -r requirements.txt
-RUN npm install
-
 EXPOSE 8000
 
-CMD gunicorn --workers=2 -b 0.0.0.0:8000 api:api
+CMD gunicorn --workers=2 -b 0.0.0.0:8000 --log-level=debug api:api

requirements.txt

 #msgpack
 #pika
 requests
-elasticsearch
+elasticsearch>=6.0.0,<7.0.0
 flask
 gunicorn
 pyyaml