![](\"https://img.serverlesscloud.cn/2020511/1589168582373-%E6%88%AA%E5%B1%8F2020-05-11%20%E4%B8%8A%E5%8D%8811.42.24.png\")
在使用云函数进行项目开发的时候，当函数数量变多后，您是否遇到函数的依赖库的管理问题？
\n由于云函数在创建或更新时，需要将函数的业务代码，和依赖库一同打包上传，因此在本地开发时，也经常是将依赖库和业务代码放置在一个文件夹下。
\n在这种情况下
\n每个云函数的代码目录下均有一套依赖库代码，而这其中有很多在若干个函数中都是重复的，不但占用了大量的空间，而且管理麻烦，在某些依赖库需要进行升级时，要进入到每个函数项目中去检查依赖关系和升级操作。
\n另一方面，这些依赖库通常不会有大的变动，但是却需要在每次函数进行更新时，都要和业务代码一同打包上传，导致实际的代码更新可能就一两行，但是需要生成一个十几兆甚至几十兆的包去上传，在网络环境不好的情况下还需要忍受缓慢的上传速度。
\n近期，腾讯云的 SCF 云函数推出了层功能，是为了这类不经常变动的依赖库或静态文件而准备的产品功能。
\n通过使用层功能来存储及管理依赖库，并在使用时按需与函数进行绑定，就可以实现依赖库的多函数共享，仅需上传一份，就可以在多个要使用到的函数中绑定并引用。
\n通过与云函数绑定的使用方式，也就意味着不需要在云函数的业务代码中再附上相应的依赖库了，可以将业务代码和依赖库分开进行管理和部署，降低云函数每次上传时需要提交的包大小，加快上传更新的速度。
\n
层作为一个和云函数独立的资源，有独立的创建、管理流程。和函数创建类似，可以通过上传 zip 包，或者控制台上选择文件夹，或者将 zip 包提前上传 cos 后再引用的方式，来将文件内容提交到云上，并创建好层。每一个提交到层中的文件包，都将生成一个新的版本。
\n因此，在创建好一个层以后，就将具有了第一个版本；而后续如果依赖库或文件内容有升级，可以继续更新层，并生成新的版本，版本号依次增大。在创建层，或发布新版本的时候，还可以指定当前层所可支持的 runtime，这样相应 runtime 的函数，才可以浏览或绑定当前层。
\n![](\"https://img.serverlesscloud.cn/2020511/1589168582380-%E6%88%AA%E5%B1%8F2020-05-11%20%E4%B8%8A%E5%8D%8811.42.24.png\")
在使用层时，通过云函数与具体层的具体版本绑定，来实现层内容的引入和使用。在函数的配置管理界面，新增加了层的绑定配置界面。通过选择层及期望绑定的版本，就可以完成绑定操作。绑定了层以后，在函数运行时，运行环境中的 /opt 目录下就会有层的内容。当然，系统中的 NODE_PATH，PYTHONPATH 已经指定好了 /opt 目录，绑定好的层中如果包含有依赖库，在函数代码中可以直接通过 import，require 等方法直接引用，与常规写法一致，不需要额外进行路径的指定。同时，目前一个函数支持最多绑定 5 个层的版本，因此可以通过这种方法，将所需的依赖库分别引入到层中。
\n![](\"https://img.serverlesscloud.cn/2020511/1589168581412-%E6%88%AA%E5%B1%8F2020-05-11%20%E4%B8%8A%E5%8D%8811.42.24.png\")
在多个层绑定到同一个函数时，层之间有一定的顺序关系。层是按照顺序关系依次加载的，如果在相同路径下有同名文件，会产生后加载的文件覆盖先加载文件的问题，需要在此处注意多个层绑定时是否会有内容覆盖，以及加载循序是否是按自身的控制需要来的。另一方面，层与函数的绑定关系，也作为函数的配置保存。$LATEST版本的函数可以按需修改调整绑定配置，而一旦发布版本后，生成的函数版本中的配置就固定了，无法再次修改。因此，通过发布版本来固化已经开发完成的版本，可以避免函数代码或层内容的修改导致的代码不可用。
\n![](\"https://img.serverlesscloud.cn/2020511/1589168581362-%E6%88%AA%E5%B1%8F2020-05-11%20%E4%B8%8A%E5%8D%8811.42.24.png\")
在这个案例中，我们将实现一个拨测网站，并在检测到异常时发送消息到 cmq 消息队列中的云函数。这个云函数由 python 写成，将使用两个依赖库，requests 库用来实现 url 地址的 http 访问检测，及 cmq 库用来实现向 cmq 的队列发送消息。
\n在创建函数前，我将使用这两个库分别创建两个层，并在后续将函数与这两个层绑定来使用依赖库。
\n首先在本地分别创建两个文件夹： requests-lib 和 cmq-lib，通过命令行进入 requests-lib 文件夹后，执行命令
pip install requests -t在此目录下完成 requests 库的下载安装。而在 cmq-lib 文件夹内，我们通过下载或 clone https://github.com/tencentyun/cmq-python-sdk 项目，将 cmq 的 sdk 下载到本地。
\n接下来，使用这两个文件夹分别创建两个层，同样命名为 requests-lib 和 cmq-lib，通过直接选择文件夹创建，并选择好适配 runtime 为 python2。在创建完成两个层后，他们都具有版本 1可供函数绑定。
同时，我在相同地域下也创建好了名字为 testq 的 cmq 队列，并根据 sdk 需要准备好了账号 id，secret id，secret key 等信息。
接下来，我将使用如下代码创建函数 detect-sendmsg，实现 url 的拨测，并向 cmq 消息队列中发送消息
\n代码中的 appid、secretid、secretkey，需要替换为自身账号下的相关内容。
\n# -*- coding: utf8 -*-\nimport json\nimport logging\nimport os\n\nfrom cmq.account import Account\nfrom cmq.cmq_exception import *\nfrom cmq.topic import *\nimport requests\n\nlogger = logging.getLogger()\nlogger.setLevel(logging.DEBUG)\n\nprint('Loading function')\n\nappid = 1252724xxx #please change to your appid. Find it in Account Info\nsecretId = 'AKIDkkxxxxxxxxxxxxxxx' #please change to your API secret id. Find it in API secret key pair\nsecretKey = ‘xxxxxxxxxxxxxxxxxx' #please change to your API secret key. Find it in API secret key pair\nregion = u'gz'\nendpoint = 'https://cmq-queue-gz.api.qcloud.com'\n\nmy_account = Account(endpoint, secretId, secretKey)\nmy_account.set_log_level(logging.INFO)\nqueue_name = 'testq'\nmy_queue = my_account.get_queue(queue_name)\n\ntest_url_list = [\n "http://www.baidu.com",\n "http://www.qq.com",\n "http://cloud.tencent.com",\n "http://unkownurl.com"\n]\n\n\ndef test_url(url_list):\n errorinfo = []\n for url in url_list:\n resp = None\n try:\n resp = requests.get(url,timeout=3)\n except (requests.exceptions.Timeout, requests.exceptions.ConnectionError, requests.exceptions.ConnectTimeout) as e:\n logger.warn("request exceptions:"+str(e))\n errorinfo.append("Access "+ url + " timeout")\n else:\n if resp.status_code >= 400:\n logger.warn("response status code fail:"+str(resp.status_code))\n errorinfo.append("Access "+ url + " fail, status code:" + str(resp.status_code))\n if len(errorinfo) != 0:\n send_msg("拨测异常通知:"+"\\r\\n".join(errorinfo))\n\ndef send_msg(msg_body):\n try:\n logger.info("send msg"+msg_body)\n msg = Message(msg_body)\n ret_msg = my_queue.send_message(msg)\n except CMQExceptionBase as e:\n logger.warn("Send msg to queue Fail! Exception:%s\\n" % e)\n raise e\n\ndef main_handler(event, context):\n test_url(test_url_list)\n return “finish"使用此代码创建好函数，并在函数的层管理中，分别绑定好 requests-lib、cmq-lib 两个层。由于这两个层没有重复部分，因此可以以任意顺序绑定。
\n完成绑定后，可以直接通过控制台触发函数，查看运行情况。一切正常的情况下，可以看到拨测的过程，以及消息发送到消息队列中的记录。同时，也可以到消息队列的对应 queue 中，通过获取消息，获取到发送到其中的消息记录。
\n从这个例子中可以看到
\n函数代码中应用了 requests 库，和 cmq 的 sdk，但并未通过和函数一同打包上传来实现，而是将依赖库放置到层里面后，通过绑定关系来引用。通过这种方式，如果下次我们启动一个新的函数也需要使用到 requests 库，直接与已有的层绑定即可使用，而同样不需要再次打包上传。而函数代码仅一个文件，不需要带有较大的依赖库，也可以降低每次更新上传时的包大小，甚至直接快速的使用 WebIDE 来进行编辑就行。
\n层的功能为依赖库和不经常修改的静态文件提供了新的存储方案，与函数的剥离使得这类文件能够多函数复用，版本化管理；随着层功能的发展，腾讯云 Serverless team 也将进一步拓展层功能的使用，包括了在开发工具中实现自动化的层创建和绑定、层的共享、提供公共层供用户直接复用等，都已经在 roadmap 中，将在接下来的发展中逐步落地，供云函数的开发体验更加便利。
\n\n\n\n
\n\n传送门：
\n\n
\n- GitHub: github.com/serverless
\n- 官网：serverless.com
\n
欢迎访问：Serverless 中文网，您可以在 最佳实践 里体验更多关于 Serverless 应用的开发！
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第一期线上分享会如期举行！","authorslink":["https://zhuanlan.zhihu.com/ServerlessGo"],"translators":null,"translatorslink":null,"tags":["Serverless","Meetup"],"keywords":"Serverless;Serverless Framework;Tencent 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