nest.js 是 nodejs 服务运行时，要等待数据库服务启动完毕，也就是有一个启动等待的需求

https://juejin.im/entry/59a6325d6fb9a024932228e0

  
version: "2"  
services:  
  app:  
    build: ./  
    restart: always  
    ports:  
      - "5000:8000"  
    links:  
      - db  
      - redis  
    depends_on:  
      - db  
      - redis  
    environment:  
      WAIT_HOSTS: db:3306 redis:6379  

CMD ./scripts/docker/wait-for.sh && npm run deploy

  
#!/bin/bash  
  
set -e  
  
timeout=${WAIT_HOSTS_TIMEOUT:-30}  
waitAfterHosts=${WAIT_AFTER_HOSTS:-0}  
waitBeforeHosts=${WAIT_BEFORE_HOSTS:-0}  
  
echo "Waiting for ${waitBeforeHosts} seconds."  
sleep $waitBeforeHosts  
  
# our target format is a comma separated list where each item is "host:ip"  
if [ -n "$WAIT_HOSTS" ]; then  
  uris=$(echo $WAIT_HOSTS | sed -e 's/,/ /g' -e 's/\s+/\n/g' | uniq)  
fi  
  
# wait for each target  
if [ -z "$uris" ];  
  then echo "No wait targets found." >&2;  
  
  else  
  
  for uri in $uris  
  do  
    host=$(echo $uri | cut -d: -f1)  
    port=$(echo $uri | cut -d: -f2)  
    [ -n "${host}" ]  
    [ -n "${port}" ]  
    echo "Waiting for ${uri}."  
    seconds=0  
    while [ "$seconds" -lt "$timeout" ] && ! nc -z -w1 $host $port  
    do  
      echo -n .  
      seconds=$((seconds+1))  
      sleep 1  
    done  
  
    if [ "$seconds" -lt "$timeout" ]; then  
      echo "${uri} is up!"  
    else  
      echo "  ERROR: unable to connect to ${uri}" >&2  
      exit 1  
    fi  
  done  
echo "All hosts are up"  
fi  
  
echo "Waiting for ${waitAfterHosts} seconds."  
sleep $waitAfterHosts  
  
exit 0