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docker - 如何在 docker 容器中使用 cron

问题描述

我尝试在 docker 映像“jenkinsci/blueocean”中添加 crontab，但之后，jenkins 无法启动。问题可能出在哪里？非常感谢您的帮助。

<Dockerfile>

FROM jenkinsci/blueocean:1.17.0
USER root
ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.9/supercronic-linux-amd64 \
    SUPERCRONIC=supercronic-linux-amd64 \
    SUPERCRONIC_SHA1SUM=5ddf8ea26b56d4a7ff6faecdd8966610d5cb9d85
 RUN curl -fsSLO "$SUPERCRONIC_URL" \
 && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
 && chmod +x "$SUPERCRONIC" \
 && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
 && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic

ADD crontab /etc/crontab
CMD ["supercronic", "/etc/crontab"]

<crontab>
# Run every minute
*/1 * * * * echo "hello world"


commands:
$docker build -t jenkins_test .
$docker run -it -p 8080:8080 --name=container_jenkins jenkins_test

标签： dockercron

解决方案

如果使用docker inspect jenkinsci/blueocean:1.17.0你会它的入口点是：

"Entrypoint": [
    "/sbin/tini",
    "--",
    "/usr/local/bin/jenkins.sh"
],

因此，当启动容器时，它将首先执行下一个脚本。

/usr/local/bin/jenkins.sh：

#! /bin/bash -e

: "${JENKINS_WAR:="/usr/share/jenkins/jenkins.war"}"
: "${JENKINS_HOME:="/var/jenkins_home"}"
touch "${COPY_REFERENCE_FILE_LOG}" || { echo "Can not write to ${COPY_REFERENCE_FILE_LOG}. Wrong volume permissions?"; exit 1; }
echo "--- Copying files at $(date)" >> "$COPY_REFERENCE_FILE_LOG"
find /usr/share/jenkins/ref/ \( -type f -o -type l \) -exec bash -c '. /usr/local/bin/jenkins-support; for arg; do copy_reference_file "$arg"; done' _ {} +

# if `docker run` first argument start with `--` the user is passing jenkins launcher arguments
if [[ $# -lt 1 ]] || [[ "$1" == "--"* ]]; then

  # read JAVA_OPTS and JENKINS_OPTS into arrays to avoid need for eval (and associated vulnerabilities)
  java_opts_array=()
  while IFS= read -r -d '' item; do
java_opts_array+=( "$item" )
  done < <([[ $JAVA_OPTS ]] && xargs printf '%s\0' <<<"$JAVA_OPTS")

  readonly agent_port_property='jenkins.model.Jenkins.slaveAgentPort'
  if [ -n "${JENKINS_SLAVE_AGENT_PORT:-}" ] && [[ "${JAVA_OPTS:-}" != *"${agent_port_property}"* ]]; then
java_opts_array+=( "-D${agent_port_property}=${JENKINS_SLAVE_AGENT_PORT}" )
  fi

  if [[ "$DEBUG" ]] ; then
java_opts_array+=( \
  '-Xdebug' \
  '-Xrunjdwp:server=y,transport=dt_socket,address=5005,suspend=y' \
)
  fi

  jenkins_opts_array=( )
  while IFS= read -r -d '' item; do
jenkins_opts_array+=( "$item" )
  done < <([[ $JENKINS_OPTS ]] && xargs printf '%s\0' <<<"$JENKINS_OPTS")

  exec java -Duser.home="$JENKINS_HOME" "${java_opts_array[@]}" -jar ${JENKINS_WAR} "${jenkins_opts_array[@]}" "$@"
fi

# As argument is not jenkins, assume user want to run his own process, for example a `bash` shell to explore this image
exec "$@"

从上面的脚本可以看出，如果你添加CMD ["supercronic", "/etc/crontab"]到你自己的dockerfile中，那么当你的容器启动时，就等于执行next：

/usr/local/bin/jenkins.sh "supercronic" "/etc/crontab"

由于if [[ $# -lt 1 ]] || [[ "$1" == "--"* ]]; then不匹配，它会直接执行exec "$@最后一行的，这导致jenkins start code从不执行。

要修复它，您必须使用自己的docker-entrypoint.sh来覆盖其默认入口点：

码头入口点.sh：

#!/bin/bash

supercronic /etc/crontab &
/usr/local/bin/jenkins.sh

Dockerfile：

FROM jenkinsci/blueocean:1.17.0
USER root
ENV SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.9/supercronic-linux-amd64 \
    SUPERCRONIC=supercronic-linux-amd64 \
    SUPERCRONIC_SHA1SUM=5ddf8ea26b56d4a7ff6faecdd8966610d5cb9d85
RUN curl -fsSLO "$SUPERCRONIC_URL" \
 && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
 && chmod +x "$SUPERCRONIC" \
 && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
 && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic

ADD crontab /etc/crontab
COPY docker-entrypoint.sh /
RUN chmod +x /docker-entrypoint.sh
ENTRYPOINT ["/sbin/tini", "--", "/docker-entrypoint.sh"]

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