一、启动脚本分析
1、ambari的启动脚本为：service ambari-server start 或者 ambari-server start。分别对应脚本文件/etc/init.d/ambari-server 和 /usr/sbin/ambari-server，其中/usr/sbin/ambari-server文件是一个快捷方式，指向/etc/init.d/ambari-server。脚本文件/etc/init.d/ambari-server。
对应工程源码ambari-server/sbin/ambari-server，启动关键代码如下：
PYTHON_WRAP="$ROOT/usr/bin/ambari-python-wrap"
AMBARI_ENV="$ROOT/var/lib/ambari-server/ambari-env.sh"
AMBARI_PYTHON_EXECUTABLE="$ROOT/usr/sbin/ambari-server.py"
AMBARI_EXECUTABLE="$ROOT/usr/sbin/ambari-server"
case "${1:-}" in
start)
echo -e "Starting ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
stop)
echo -e "Stopping ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
reset)
echo -e "Resetting ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
restart)
echo -e "Restarting ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
upgrade)
echo -e "Upgrading ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
status)
echo -e "Ambari-server status"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
upgradestack)
echo -e "Upgrading stack of ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup)
echo -e "Setup ambari-server"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-jce)
echo -e "Updating jce policy"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-pam)
echo -e "Setting up PAM properties..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
migrate-ldap-pam)
echo -e "Migration LDAP to PAM"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-ldap)
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
sync-ldap)
echo -e "Syncing with LDAP..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
set-current)
echo -e "Setting current version..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-security)
echo -e "Security setup options..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
refresh-stack-hash)
echo -e "Refreshing stack hashes..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
backup)
echo -e "Backing up Ambari File System state... *this will not backup the server database*"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
restore)
echo -e "Restoring Ambari File System state"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
update-host-names)
echo -e "Updating host names"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
check-database)
echo -e "Checking database"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
enable-stack)
echo -e "Enabling stack(s)..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-sso)
echo -e "Setting up SSO authentication properties..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
db-purge-history)
echo -e "Purge database history..."
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
install-mpack)
echo -e "Installing management pack"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
uninstall-mpack)
echo -e "Uninstalling management pack"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
upgrade-mpack)
echo -e "Upgrading management pack"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
setup-kerberos)
echo -e "Setting up Kerberos authentication"
$PYTHON "$AMBARI_PYTHON_EXECUTABLE" "$@"
;;
*)
echo "Usage: $AMBARI_EXECUTABLE
{start|stop|reset|restart|upgrade|status|upgradestack|setup|setup-jce|setup-ldap|sync-ldap|set-current|setup-security|refresh-stack-hash|backup|restore|update-host-names|check-database|enable-stack|setup-sso|db-purge-history|install-mpack|uninstall-mpack|upgrade-mpack|setup-kerberos|setup-pam|migrate-ldap-pam} [options]
Use $AMBARI_PYTHON_EXECUTABLE <action> --help to get details on options available.
Or, simply invoke ambari-server.py --help to print the options."
exit 1
esac2. 从上图中可以看出，执行/etc/init.d/ambari-server start 命令，脚本会调用python执行/usr/sbin/ambari-server.py 脚本文件，对应源码ambari-server/src/main/python/ambari-server.py，ambari-server.py 脚本解析传入的命令行参数，然后执行 main(options, args, parser) 方法，核心代码如下：
@OsFamilyFuncImpl(OsFamilyImpl.DEFAULT)
def create_user_action_map(args, options):
action_map = {
SETUP_ACTION: UserAction(setup, options),
START_ACTION: UserAction(start, options),
STOP_ACTION: UserAction(stop, options),
}
return action_map
def main(options, args, parser):
action_map = create_user_action_map(args, options)
action = args[0]
try:
action_obj = action_map[action]
except KeyError:
parser.error("Invalid action: " + action)
action_obj.execute()
此时args值是['start']，options值为空，START_ACTION是一个常量，其值在setupActions.py文件中定义：START_ACTION = "start"．调用action_obj.execute()方法实际是调用了 UserAction(start, options) 对象的方法：
class UserActionPossibleArgs(object):
def __init__(self, i_fn, i_possible_args_numbers, *args, **kwargs):
self.fn = i_fn
self.possible_args_numbers = i_possible_args_numbers
self.args = args
self.kwargs = kwargs
self.need_restart = False
def execute(self):
self.fn(*self.args, **self.kwargs)
class UserAction(UserActionPossibleArgs):
def __init__(self, i_fn, *args, **kwargs):
super(UserAction, self).__init__(i_fn, [1], *args, **kwargs)
从上面代码中可以看出，execute()方法去调用fn()方法，但是fn变量是由外部传入的，传入值为start，因此会去调用start()方法，start()方法代码如下：
@OsFamilyFuncImpl(OsFamilyImpl.DEFAULT)
def start(args):
status, pid = is_server_runing()
if status:
err = "Ambari Server is already running."
raise FatalException(1, err)
server_process_main(args)
3. server_proecess_main()方法在/usr/sbin/ambari-server-main.py文件中定义，对应源码ambari-server/src/main/python/ambari-server-main.py。server_process_main()方法源码如下：
CHECK_DATABASE_HELPER_CMD = "{0} -cp {1} org.apache.ambari.server.checks.DatabaseConsistencyChecker"
def server_process_main(options, scmStatus=None):
jdk_path = find_jdk()
properties = get_ambari_properties()
ensure_jdbc_driver_is_installed(options, properties)
ensure_dbms_is_running(options, properties, scmStatus)
refresh_stack_hash(properties)
java_exe = get_java_exe_path()
environ = generate_env(options, ambari_user, current_user)
class_path=serverClassPath.get_full_ambari_classpath_escaped_for_shell(
validate_classpath=True)
command = CHECK_DATABASE_HELPER_CMD.format(java_exe, class_path)
(retcode, stdout, stderr) = run_os_command(command, env=environ)
update_properties(properties)
param_list = generate_child_process_param_list(ambari_user, java_exe,
class_path, debug_start, suspend_mode,options)
print_info_msg("Running server: " + str(param_list))
procJava = subprocess.Popen(param_list, env=environ,
preexec_fn=make_process_independent)
pidfile = os.path.join(configDefaults.PID_DIR, PID_NAME)
save_pid(pidJava, pidfile)
wait_for_server_start(pidfile, scmStatus)
return procJava
get_ambari_properties()方法去加载ambari.properties文件，默认位于/etc/ambari-server/conf目录下，将其转化为 Properties 对象．
4. refresh_stack_hash()方法是去刷新stack目录下文件夹hash值：在 /var/lib/ambari-server/resources/stacks/xxx/xxx/services 目录下，集成了关于各个组件的元信息，控制脚本及配置文件，以HDFS服务为例，其文件夹内容如下：
该目录下的package文件夹存放了组件启停控制脚本文件，在agent端执行组件启停命令时，也是先将该文件夹拷贝到自己节点的cache目录下，然后执行对应脚本，package文件夹内容如下：
该文件夹有两个特别的文件archive.zip和.hash，archive.zip文件是对alerts，files，scripts，templates４个文件夹压缩而产生的压缩包，.hash文件存放archive.zip文件的hash值．agent端拷贝package文件夹时，只拷贝了archive,zip文件和.hash文件．当修改了package文件夹下的文件内容时，ambari-server进程重启会重新生成archive.zip文件和.hash文件，而agent端在执行命令时，会先去比对两个.hash文件内容是否一致，如果不一致，则重新拷贝这两个文件到cache目录下．
5. 接下来的代码是去执行数据库的数据一致性检测：
command = CHECK_DATABASE_HELPER_CMD.format(java_exe, class_path)
(retcode, stdout, stderr) = run_os_command(command, env=environ)
它调用了org.apache.ambari.server.checks.DatabaseConsistencyChecker类的main()方法进行数据库一致性检测，防止数据错乱的问题．
6. 接着方法调用了generate_child_param_list()方法生成命令参数列表，该方法主要逻辑如下：
SERVER_START_CMD = "{0} " \
"-server -XX:NewRatio=3 " \
"-XX:+UseConcMarkSweepGC " + \
"-XX:-UseGCOverheadLimit -XX:CMSInitiatingOccupancyFraction=60 " \
"-XX:+CMSClassUnloadingEnabled " \
"-Dsun.zip.disableMemoryMapping=true " + \
"{1} {2} " \
"-cp {3} "\
"org.apache.ambari.server.controller.AmbariServer {4}" \
"> {5} 2>&1 || echo $? > {6}"
@OsFamilyFuncImpl(OsFamilyImpl.DEFAULT)
def generate_child_process_param_list(ambari_user, java_exe, class_path,
debug_start, suspend_mode,options=None):
from ambari_commons.os_linux import ULIMIT_CMD
properties = get_ambari_properties()
command_base = SERVER_START_CMD_DEBUG if debug_start else SERVER_START_CMD
command = command_base.format(java_exe,
ambari_provider_module_option,
jvm_args,
class_path,
startMode,
configDefaults.SERVER_OUT_FILE,
os.path.join(configDefaults.PID_DIR, EXITCODE_NAME),
suspend_mode)
param_list.append(cmd)
return param_list
generate_child_param_list()方法里最主要的是格式化SERVER_START_CMD命令来生成启动子进程的param_list，从该命令中得出Java程序入口类是org.apache.ambari.server.controller.AmbariServer。
接下来便是启动java子进程的代码：
print_info_msg("Running server: " + str(param_list))
procJava = subprocess.Popen(param_list, env=environ,
preexec_fn=make_process_independent)
pidfile = os.path.join(configDefaults.PID_DIR, PID_NAME)
save_pid(pidJava, pidfile)
wait_for_server_start(pidfile, scmStatus)
return procJava
方法调用python的subprocess模块启动子进程，然后保存pid到文件中，等待进程成功启动后返回，至此整个启动流程结束。
