Migrate Flask server between containers

README.md

Example:

docker-compose up -d nginx web1

curl http://10.0.0.4

docker-compose exec web1 sh -c 'criu dump -t $(pidof python3) -j -D /mnt --tcp-established'
docker-compose up -d web2

curl http://10.0.0.4

app.py

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello world!\n"

if __name__ == "__main__":
    app.run(host="0.0.0.0", port=80)

docker-compose.yml

version: "2.4"

services:
  web1:
    privileged: true
    build: .
    expose:
      - "80"
    volumes:
      - "checkpoint:/mnt"
    networks:
      app_net:
        ipv4_address: 10.0.0.2

  web2:
    command: criu restore -D /mnt --tcp-established
    privileged: true
    build: .
    expose:
      - "80"
    volumes:
      - "checkpoint:/mnt"
    networks:
      app_net:
        ipv4_address: 10.0.0.3

  nginx:
    image: nginx:stable-alpine
    volumes:
      - ./nginx.conf:/etc/nginx/nginx.conf:ro
    ports:
        - "80:80"
    networks:
      app_net:
        ipv4_address: 10.0.0.4

networks:
  app_net:
    driver: bridge
    ipam:
      driver: default
      config:
      - subnet: 10.0.0.0/24
        gateway: 10.0.0.1

volumes:
  checkpoint:

Dockerfile

FROM ubuntu:18.04 as build

RUN apt-get update -qq
RUN apt-get install -qq \
	libnet-dev \
	libnl-route-3-dev \
	gcc \
	bsdmainutils \
	build-essential \
	git-core \
	iptables \
	libbsd-dev \
	libaio-dev \
	libcap-dev \
	libgnutls28-dev \
	libgnutls30 \
	libnl-3-dev \
	libprotobuf-c-dev \
	libprotobuf-dev \
	libselinux-dev \
	pkg-config \
	protobuf-c-compiler \
	protobuf-compiler \
	python3-minimal \
	python3-distutils \
	asciidoctor \
	curl

RUN git clone --depth 1 https://github.com/checkpoint-restore/criu/ /usr/src/criu \
    && cd /usr/src/criu \
    && make -j $(nproc) \
    && make install PREFIX=/usr \
    && rm -rf /usr/src/criu

RUN apt-get install -qq python3-flask
COPY app.py /app.py
CMD python3 app.py

nginx.conf

user  nginx;
worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
    worker_connections  1024;
}

http {
    upstream web {
        server 10.0.0.2:80;
        server 10.0.0.3:80;
    }

    server {
	listen 80;

	location / {
        	proxy_pass http://web;
   	 }
    }
}