利用 Kubernetes 部署简单的 Python 应用程序！

2019-04-07 本文已影响0人 14e61d025165

Kubernetes 推出已有数年（初始发行版可追溯至 2014 年 6 月），虽然其强大的功能早已为程序员社群所熟知并认可，但很多人仍然尚未使用。如果您还没有使用过 Kubernetes，这并不稀奇。我曾听闻一些开发者说过，让他们踌躇不前的原因包括：没有真正合适的指南可供使用（大量文章分散于多个网站，而不是集中于一处），或者他们对学习新事物感到畏惧。在本教程中，我将通过利用 Docker 构建 Python 应用程序并将其部署到 Kubernetes 服务这一基本理念，帮助您一定程度上化繁为简。

学习目标

完成本教程后，您将能够：

通过使用 Docker 实现 Flask 应用程序容器化，并将其部署至 IBM Cloud Kubernetes Service。

前提条件

免费试用 IBM Cloud

利用IBM Cloud Lite 快速轻松地构建您的下一个应用程序。您的免费帐户从不过期，而且您会获得 256 MB 的 Cloud Foundry 运行时内存和包含 Kubernetes 集群的 2 GB 存储空间。了解所有细节并确定如何开始。如果您不熟悉 IBM Cloud，请查阅 developerWorks 上的 IBM Cloud Essentials 课程。

为完成本教程，您需要具备以下前提条件：

一个 IBM Cloud™ 帐户 -（注册免费帐户）
IBM Cloud CLI
Docker CLI
Kubernetes CLI

预计花费时间

完成本教程大约需要 45 分钟。

步骤

创建 Kubernetes 集群

登录 IBM Cloud Dashboard 。
打开 IBM Kubernetes Service 。

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单击 Create Cluster 。

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选择要部署集群的区域 ( Region )，输入集群的名称 ( name )，然后单击 Create Cluster 。
根据您的帐户（ Paid 或 Free ），选择相应的集群类型。
集群需要一些时间才能准备就绪（约 30 分钟）。

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集群准备就绪后，单击集群名称，这样会将您重定向至包含集群和工作节点相关信息的新页面。

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单击 Worker Nodes 选项卡以记录集群的公共 IP。

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实现 Flask 应用程序的容器化

在项目目录中，创建名为 "Dockerfile" 的文件。 建议：将您的文件准确命名为 "Dockerfile"，而不使用其他任何字符。

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"Dockerfile" 用于向 Docker 指示基本镜像、所需 Docker 设置，以及为准备和启动新容器您希望已执行的命令列表。
在此文件中，粘帖以下代码：

<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">FROM python:2.7
LABEL maintainer="Kunal Malhotra, kunal.malhotra1@ibm.com"
RUN apt-get update
RUN mkdir /app
WORKDIR /app
COPY . /app
RUN pip install -r requirements.txt
EXPOSE 5000
ENTRYPOINT [ "python" ]
CMD [ "app.py" ]
</pre>

以上 Dockerfile 代码的说明和分解

以上代码的第一部分为：

由于此 Flask 应用程序使用 Python 2.7，我们需要支持并且已安装该程序的环境。幸运的是，DockerHub 具有在 Ubuntu 之上安装的官方镜像。只需一行代码即可获取包含 Python 2.7、virtualenv 和 pip 的基本 Ubuntu 镜像。DockerHub 上有大量镜像，但只要您愿意，您也可以从全新 Ubuntu 镜像开始，并在此基础上进行构建。
让我们来看下一段代码：

<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">LABEL maintainer="Kunal Malhotra, kunal.malhotra1@ibm.com"
RUN apt-get update
</pre>

记录维护程序，并更新 Ubuntu 程序包索引。命令为 RUN，此函数用于运行它后面的命令。

现在即可将 Flask 应用程序添加到镜像中。为简便起见，将应用程序复制到 Docker 镜像上的 /app 目录下。
WORKDIR 本质上是 Bash 中的 cd ，而 COPY 则会将某个目录复制到镜像中提供的目录。ADD 命令与 COPY 执行相同的操作，但它允许您从 URL 添加存储库。因此，如果您要克隆自己的 git 存储库，而不是从本地存储库进行复制（用于登台和生产目的），那么可以使用该命令。除非您有 URL，否则大部分情况下应使用 COPY。
既然我们已将存储库复制到镜像，接下来就将安装所有依赖项，代码的 requirements.txt 部分中对此进行了定义。

<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">RUN pip install --no-cache-dir -r requirements.txt
</pre>

我们使用 EXPOSE 来公开用于运行 Flask 应用程序的端口 (5000)。

ENTRYPOINT 用于指定应用程序的入口点。

从 Dockerfile 构建镜像

打开终端，并输入以下命令以从 Dockerfile 构建镜像： docker build -t <image_name>:<tag> . （注意句点，它指示我们位于应用顶层目录中）。例如： docker build -t app:latest .

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在本地运行容器并进行测试

成功构建镜像后，输入： docker run -d -p 5000:5000 app

此命令将创建一个包含镜像中所有应用程序代码和依赖项的容器，并在本地运行该容器。

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将镜像推送至 IBM Cloud Registry

从帐户仪表板转至 IBM Cloud Kubernetes Service 。
在左侧导航菜单中选择 Private Repositories 。

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image

安装 Container Registry 插件。
ibmcloud plugin install container-registry -r Bluemix
登录到您的 IBM Cloud 帐户。
ibmcloud login -a <cloud_foundary_end_point_for_the_region>
命名并创建名称空间。快速入门的其余部分都将使用此名称空间。
ibmcloud cr namespace-add <namespace>
将本地 Docker 守护程序登录到 IBM Cloud Container Registry 中。
ibmcloud cr login
选择存储库和用于识别镜像的标签。
docker tag <image_name> <region_url>/<namespace>/<image_name>:<tag>
推送镜像。
docker push <region_url>/<namespace>/<image_name>:<tag>

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image

验证您的镜像是否位于专用注册表中。
ibmcloud cr image-list

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为 Kubernetes 创建配置文件

将镜像成功上传至专用注册表后，转至项目目录并创建以下两个文件： Deployment.yaml 和 service.yaml 。

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在 deployment.yaml 文件中，粘帖以下代码：

<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: flask-node-deployment
spec:
replicas: 1
selector:
matchLabels:
app: flasknode
template:
metadata:
labels:
app: flasknode
spec:
containers:
- name: flasknode
image: registry.ng.bluemix.net/flask-node/app
imagePullPolicy: Always
ports:
- containerPort: 5000
</pre>

在 service.yaml 文件中，粘帖以下代码：

<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">apiVersion: v1
kind: Service
metadata:
name: flask-node-deployment
spec:
ports:

port: 5000
targetPort: 5000
selector:
app: flasknode
</pre>

Deployment.yaml 代码的说明和分解

创建名为 flask-node-deployment 的部署，此部署由 .metadata.name 字段来指示。
此部署会创建一个复制 pod，由 replicas 字段来指示。
Selector 字段用于定义部署查找要管理的 pod 的方式。在此情况下，我们只需选择 Pod 模板中定义的一个标签即可 (app: flasknode )。但是，也可以使用更复杂的选择规则，只要 Pod 模板本身满足此规则即可。
Pod 模板规范 .template.spec 指示 pod 在运行容器 flasknode，该容器运行应用专用注册表镜像。
该部署会打开 port 5000 以供 Pod 使用。

Service.yaml 代码的说明和分解

Service.yaml 规范将创建名为 flask-node-deployment 的新服务对象，目标为具有 "app=flasknode" 标签的任意 Pod 上的 TCP 端口 5000。同时还会为此服务分配 IP 地址（有时称为集群 IP），供服务代理使用（请参阅下文）。将持续评估此服务的选择器，并将结果通过 POST 操作发布到同样名为 flask-node-deployment 的端点对象。
须注意，此服务可将传入端口映射到任意 targetPort。默认情况下，targetPort 将设置为与 port 字段相同的值。可能更有趣的是，targetPort 可以是字符串，表示后端 Pod 中的端口名称。分配给该名称的实际端口号可与每个后端 Pod 中的端口号不同。这就为服务部署和演变提供了诸多灵活性。例如，您可在后端软件的下一个版本中更改 Pod 公开的端口号，而无需中断客户端。

将应用程序部署至 Kubernetes

锁定要在其中工作的 IBM Cloud Kubernetes Service 区域。
ibmcloud cs region-set us-south
在 CLI 中为集群设置上下文。

export KUBECONFIG=/Users/$USER/.bluemix/plugins/container-service/clusters/< cluster_name >/< cluster_configuration_file.yaml>
</pre>

列出您的工作节点，验证您是否可以连接到自己的集群。
kubectl get nodes
创建部署。
kubectl create -f deployment.yaml

利用 Kubernetes 部署简单的 Python 应用程序！

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