无法在 docker 入口点脚本中捕获信号

Question

我有一个 docker 入口点脚本，它应该捕获发送到容器中进程的信号。主要应用程序是 tomcat - java 进程嵌入在 docker-entrypoint.sh 中，传递给 dumb-init。容器中的进程映射如下所示：

root@mycontainer:/usr/local/tomcat/webapps/datarouter-example# ps -ef
    UID        PID  PPID  C STIME TTY          TIME CMD
    root         1     0  0 05:21 ?        00:00:00 dumb-init -- /docker-entrypoint.sh
    root         6     1  0 05:21 ?        00:00:00 bash /docker-entrypoint.sh
    root        14     6  1 05:21 ?        00:08:57 /jdk-13.0.1/bin/java -Djava.util.logging.config.file=....

Docker 文件：

FROM maven:3.6.3-jdk-13 as maven_builder

WORKDIR /app
COPY . /app
RUN ["mvn","clean","install","-T","2C","-DskipTests=true"]


FROM tomcat:9.0.31-jdk13-openjdk-buster

ARG dumbInitVersion='1.2.2'

# install dependencies
RUN apt-get update && apt-get install -y --no-install-recommends \
        sudo \
        wget \
        dpkg-dev \
    && rm -rf /var/lib/apt/lists/*

ARG webappDir
WORKDIR $CATALINA_HOME/webapps/$webappDir/
ENV CATALINA_OUT $CATALINA_HOME/logs/catalina.out
ENV CATALINA_PID $CATALINA_HOME/catalina.pid
COPY docker-entrypoint.sh /
COPY --from=maven_builder /app/target/datarouter-example $CATALINA_HOME/webapps/$webappDir/

RUN wget https://github.com/Yelp/dumb-init/releases/download/v"$dumbInitVersion"/dumb-init_"$dumbInitVersion"_amd64.deb; \
    dpkg -i dumb-init_*.deb; \
    rm dumb-init_*.deb

EXPOSE 8080
ENTRYPOINT ["dumb-init", "--", "/docker-entrypoint.sh"]

这是简化的 docker-entrypoint.sh:

        #!/usr/bin/env bash

        start(){
                echo "$(date +'%F %T,%3N') Starting tomcat..." >> "$CATALINA_OUT"
                catalina.sh start && tail -f "$CATALINA_OUT"
        }

        stop(){
                echo "$(date +'%F %T,%3N') starting stop" >> "$CATALINA_OUT"

   # some fancy shutdown logic, e.g. calling our application's shutdown endpoint to cleanup (does not stop tomcat)

                echo "$(date +'%F %T,%3N') Stopping tomcat..." >> "$CATALINA_OUT"
                catalina.sh stop  >> "$CATALINA_OUT"

                wait $(cat "${CATALINA_PID}")

                tailId=$(pgrep tail)
                if [[ -n "$tailId" ]]; then
                        kill "$tailId"
                fi
                exit
        }

        trap stop SIGINT SIGQUIT SIGHUP SIGTERM

    start

现在是问题。每次从容器内部发出 docker stop 命令或 kill 1 时， java 应用程序都会收到一个信号，并在 stop 函数获取之前首先开始关闭到第一行。我确定是因为 Terminated 日志：

Terminated
++ stop
+++ date '+%F %T,%3N'
++ echo '2020-03-13 14:34:54,480 starting stop'

并在 catalina.out 中：

2020-03-12 04:08:27.079 INFO [Thread-13] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["http-apr-8080"]
2020-03-12 04:08:27,079 starting stop
2020-03-12 04:08:27.085 INFO [Thread-13] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["http-apr-8081"]
2020-03-12 04:08:27.090 INFO [Thread-13] org.apache.coyote.AbstractProtocol.pause Pausing ProtocolHandler ["https-openssl-apr-8443"]
2020-03-12 04:08:27.096 INFO [Thread-13] org.apache.catalina.core.StandardService.stopInternal Stopping service [Catalina]
......

我真的很困惑为什么会发生这种情况以及如何解决这个问题以便 catalina.sh stop 得到执行。

Answer 1

尝试一些更改后，以下脚本捕获 SIGTERM 并执行预期的步骤。

原始 docker-entrypoint、Dockerfile 的变化：

从 dumb-init 切换到 tini，只是为了尝试一下。
从 catalina start 切换到 catalin 运行并自己将其置于后台并等待它
删除尾进程

我认为尾巴是导致最初描述的行为的原因。新入口点脚本的最大缺点是我在运行宁 docker logs ... 时丢失了容器日志。由于我们绑定挂载日志目录，我们仍然能够获取日志，但将进一步调查以取回 docker logs ...

如果有人有建议或其他解决方案，我仍在寻找更好的解决方案。

#!/usr/bin/env bash

trap stop SIGTERM SIGINT SIGQUIT SIGHUP ERR

start(){
   local catalinaPid

   touch "${CATALINA_PID}"
   catalina.sh run >> ${CATALINA_OUT} 2>&1 &
   catalinaPid=$!
   echo "$catalinaPid" > "${CATALINA_PID}"

   wait "$catalinaPid"
}

stop(){
   echo "$(date +'%F %T,%3N') starting stop" >> "$CATALINA_OUT"

   # some fancy shutdown logic, e.g. calling our application's shutdown endpoint to cleanup (does not stop tomcat)

   echo "$(date +'%F %T,%3N') Stopping tomcat..." >> "$CATALINA_OUT"
   catalina.sh stop 20 >> "$CATALINA_OUT"

   wait $(cat "${CATALINA_PID}")

   exit
}

start

无法在 docker 入口点脚本中捕获信号

Unable to trap signals in docker entrypoint script

docker

wait

tomcat9

sigterm

bash-trap