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 "${1:-}" instart)echo -e "Starting ambari-server"$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
esac

2. 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_mapdef 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_fnself.possible_args_numbers = i_possible_args_numbersself.args = argsself.kwargs = kwargsself.need_restart = Falsedef 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_CMDproperties = get_ambari_properties()command_base = SERVER_START_CMD_DEBUG if debug_start else SERVER_START_CMDcommand = 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。

二、java启动流程