Java Runtime Environment

info

This article serves as a thorough introduction to Cloud Engine’s Java runtime environment. To quickly get started with Cloud Engine, see Getting Started With Cloud Engine.

You can deploy WAR and JAR projects built with Maven to Cloud Engine, or upload WAR files directly to Cloud Engine.

If you are looking to start a new project, we recommend that you use one of our sample projects as a boilerplate:

caution

Running a Java program usually costs a large amount of memory. If you are using a trial instance with 256M of memory, Cloud Engine might encounter an OOM error when starting your Java program, causing your deployment to fail. Even if Cloud Engine is able to start your program, the program might frequently get restarted due to low memory.

We recommend that you pick an instance with at least 512 MB of memory. If your project is built with Spring Boot, a minimum of 1024 MB of memory is recommended. You can adjust the memory size at any time even if you've already deployed your project. See Cloud Engine Platform Features § Adjusting Quota and Number of Instances for more information on how to adjust the memory size of your instances.

Startup Command

Once the build is finished, Cloud Engine will look for a .war or .jar file under target:

If it finds a .war file, it will place the file into a Servlet container (Jetty 9.x).
If it finds a .jar file, it will run the file with java -jar.

Configure JVM Parameters

When Cloud Engine runs a Java application, it will give -Xmx a value equivalent to 70% of the size of the instance. The remaining 30% will be reserved for off-heap memory and other consumptions. You may customize the value of -Xmx if your application has special needs (like using a large amount of off-heap memory). For example, if your instance has a memory of 2 GB, you can add a custom environment variable on Cloud Engine’s Settings page with JAVA_OPTS as its name and -Xmx1500m as its value. This will limit the size of the JVM heap to 1.5 GB and leave 500 MB for PermGen, off-heap memory, and other stuff. Keep in mind that if the value of -Xmx is too small, a large amount of CPU might be wasted on repetitive garbage collection tasks.

Configure Java Version

To specify the Java version you want to use, create a file named system.properties under the root directory of your project:

system.properties

java.runtime.version=11

At this time, Cloud Engine supports AdoptOpenJDK 8, 11, 12, 13, and 14.

note

For newly created apps, if you don’t specify a Java version, the latest stable (LTS) version will be used. For apps created before 9/2/2021, Java `8` will be used by default to ensure compatibility.

Upload WAR File

If you’ve already built the WAR file on your local computer (with commands like mvn package), you can add the --war option when you deploy your project with the CLI. This tells the CLI to upload the WAR file rather than the source code.

lean deploy --war

In this case, Cloud Engine won’t install dependencies or build your project on the server side. Instead, it will run the WAR file by placing it into a Servlet container.

Install Dependencies and Build

If you’ve uploaded the source code, Cloud Engine will install the dependencies listed in pom.xml with Maven and build your project by running mvn package.

Customize Build Process

Cloud Engine uses the default commands of each language to complete the build process. You can override these commands by editing leanengine.yaml.

Overriding Command for Execution With `run`

leanengine.yaml
run: $(npm bin)/serve -c static.json -l ${LEANCLOUD_APP_PORT}

You can use shell syntax here for purposes like accessing environment variables.

Overriding Command for Installing Dependencies With `install`

You can override the default command for installing dependencies (like npm install) or run additional commands before or after installing dependencies.

leanengine.yaml
install: npm

Most runtimes have their default commands for installing dependencies. You can refer to the default command with {use: 'default'}:

leanengine.yaml
install:
  - { use: "default" }
  - npm run install-additional

When installing dependencies, only the dependency lists (like package.json) will be loaded into the build directory. To load additional files, use require:

leanengine.yaml
install:
  - require:
      - frontend/package.json
      - frontend/package-lock.json
  - cd frontend && npm ci

Overriding Command for Building With `build`

leanengine.yaml
build: npm run build

When building your project, all the files in your project will be loaded into the build directory.

You can specify multiple pieces of commands with an array. You can use shell syntax here as well:

leanengine.yaml
build:
  - echo 'building'
  - NODE_ENV=production $(npm bin)/webpack

Certain runtimes have their default build commands. You can refer to these commands with {use: 'default'}.

Build Logs

By default, the logs generated during the build process won’t be printed to the console. If the build process fails, the logs from the last completed step will be printed to the console.

To print the complete build log for debugging, check Print build logs if you are deploying from the dashboard or add --options 'printBuildLogs=true' if you are deploying with the CLI.

System Dependencies

You can specify the system dependencies provided by the server-side environment by setting systemDependencies in leanengine.yaml:

leanengine.yaml
systemDependencies:
  - imagemagick

The following libraries are available for you to add:

ffmpeg A library for processing audio and videos.
imagemagick A library for processing images.
fonts-wqy 文泉驿点阵宋体 and 文泉驿微米黑. Often used with phantomjs or chrome-headless to display Chinese.
fonts-noto Source Han Sans (comes with a large size).
phantomjs A headless browser based on WebKit (discontinued).
chrome-headless Headless Chrome. It comes with a large size and will significantly increase the time needed for deployment. It also consumes a lot of CPU and RAM resources. If you need to use puppeteer, please provide {executablePath: '/usr/bin/google-chrome', args: ['--no-sandbox', '--disable-setuid-sandbox']} to puppeteer.launch. This library doesn’t support Java yet.
node-canvas The system dependency required for installing node-canvas (you still need to install node-canvas yourself).
python-talib A library for performing technical analysis of financial market data.

caution

Adding system dependencies will significantly increase the time needed for deployment. Please avoid adding dependencies that your project doesn’t need.

Health Check

Cloud Engine is primarily optimized for web applications. Your app is expected to provide HTTP services through the port specified by the environment variable named LEANCLOUD_APP_PORT. Keep in mind that the app should listen on 0.0.0.0 (all interfaces) instead of 127.0.0.1 which is the default host of many frameworks.

While your app is being deployed, Cloud Engine will check your app every second to see if it has been successfully started. If your app has not been started within the time limit (30 seconds by default), the deployment will be canceled. After your app has been deployed, Cloud Engine will run health checks for your app regularly and automatically restart it if the check fails.

The way the health check works is that Cloud Engine will send an HTTP request to the homepage (/) of your app. If it gets an HTTP 2xx response, your app will pass the health check.

Health check and the Cloud Engine SDK

Cloud Engine will also check /__engine/1/ping which is handled by the SDK. If the SDK is integrated correctly, Cloud Engine will not check the homepage (/) anymore.

If Dashboard > LeanEngine > Your group > Settings > Cloud functions mode is set to Enable, or if functionsMode in leanengine.yaml is set to strict, Cloud Engine will check if the SDK is integrated correctly. If not, it will consider your app to have failed to start.

Customizing startup timeout (startupTimeout)

The default timeout for your app to start is 30 seconds. You can change it to any value between 15 and 120 seconds with leanengine.yaml:

leanengine.yaml
startupTimeout: 60

Cloud Environment

Custom Domains

Projects deployed to Cloud Engine can only be accessed with domains configured. You can bind domains by going to Dashboard > LeanEngine > Your group > Settings > Domains.

If you bind a domain that starts with stg- (e.g., stg-api.example.com), it will be assigned to the staging environment automatically.

Load Balancer and CDN

All HTTP and HTTPS requests sent to Cloud Engine will go through a load balancer that deals with chores including HTTPS encryption, HTTPS redirection, and response compression. You won’t have to implement features for handling these tasks yourself for the programs hosted on Cloud Engine. Meanwhile, the load balancer brings the following restrictions that your program cannot bypass:

Paths starting with /.well-known/acme-challenge/ are used by Cloud Engine to automatically renew certificates. Requests sent to these paths won’t be forwarded to your program.
The size of a request header (URL and headers) should be within 64K and each line of the request header should be within 8K.
The size of a request (for uploading files) should be within 100M.
The timeout for connecting or waiting for a response is 60 seconds.

Getting the Client IP Address

Cloud Engine’s load balancer includes the following information depicting the original request in the HTTP header:

X-Real-IP: The original IP address.
X-Forwarded-Proto: The original protocol (http or https).
Forwarded: Information about the proxy, defined by RFC 7239. It contains the IP address and the protocol.

caution

If CDN is enabled, the information included in the HTTP headers above will be those of the CDN rather than the original request.

With CDN enabled, the following HTTP headers will also be present:

X-Forwarded-For: IP addresses separated by a comma. The first one would be the IP address of the original request.

caution

It’s possible that the information included in the HTTP headers above gets counterfeited. Cloud Engine won’t be able to guarantee its authenticity.

EngineRequestContext.getRemoteAddress();

info

For Cloud Engine applications deployed within Mainland China, CDN will be enabled by default. To ensure that your application always gets the accurate IP addresses of original requests, consider enabling dedicated IP. You can learn more about the differences between CDN and dedicated IP on Binding Your Domains § Cloud Engine Domains.

HTTPS Redirect

When you bind a custom Cloud Engine domain, you can enable Force HTTPS to have the load balancer redirect HTTP requests to HTTPS while keeping the paths.

caution

Force HTTPS won’t work properly if CDN is enabled. You’ll still need to implement redirect in your project’s code.

CDN Caching

If you resolve your custom domain to the CDN (including the shared domain provided by Cloud Engine), the CDN will cache the responses for the requests it has received. There are some default rules for caching followed by the CDN.

The CDN will cache the response if:

The response header contains Last-Modified (this indicates that the resource requested is static; for HTML files, they will be cached for at most 60 seconds).

The CDN will not cache the response if:

There is an error with the response (not 2xx).
The request is not idempotent (like a POST request).
The response header doesn’t contain Last-Modified (this often indicates that the resource requested is dynamic).

The age of the cache for a given file will depend on the file type and the value of the Last-Modified header. The less frequently the file gets modified, the longer the file gets cached. You can override the default behavior by configuring Cache-Control and the CDN will try its best to follow your configurations. For example:

You can use Cache-Control: no-cache to prevent the response from being cached.
You can use Cache-Control: max-age=3600 to specify the age of the cache (here we set it to be 1 hour).

info

To prevent your application from being affected by the caching mechanism, consider enabling dedicated IP. You can learn more about the differences between CDN and dedicated IP on Binding Your Domains § Cloud Engine Domains.

Environment Variables

The following environment variables are available for your application to use:

Variable name	Description
`LEANCLOUD_APP_ID`	The `App ID` of the current application.
`LEANCLOUD_APP_KEY`	The `App Key` of the current application.
`LEANCLOUD_APP_MASTER_KEY`	The `Master Key` of the current application.
`LEANCLOUD_APP_ENV`	The environment your application is running in. If you are running your application on your local computer, the value will be non-existent or `development` (if you are starting your application with the CLI). It will be `stage` for the staging environment and `production` for the production environment.
`LEANCLOUD_APP_PORT`	The port opened up for your application. Your application has to listen on this port in order for users to access your service.
`LEANCLOUD_API_SERVER`	The address used to access the Data Storage service. Please use this value if your application needs to access the Data Storage service or other cloud services with the REST API.
`LEANCLOUD_APP_GROUP`	The group the instance is located at.
`LEANCLOUD_REGION`	The region the application is running in. It will be `CN` for Mainland China and `US` for the United States.
`LEANCLOUD_VERSION_TAG`	The version number of the deployment.

The environment variables starting with LC_ (like LC_APP_ID) used by the older version of Cloud Engine have already been deprecated. Those environment variables will still be present for a while to ensure compatibility but will eventually get removed. If you are still using them in your application, please replace them with those starting with LEANCLOUD_.

Logs

note

See Cloud Engine Platform Features § Viewing Logs for more information on how to view logs and access logs on the dashboard.

Cloud Engine will collect the logs your application has printed to standard output (stdout) and standard error (stderr):

note

Each line of the logs can contain a maximum of 4096 characters. A maximum of 600 lines of logs can be collected every minute. The logs generated by your application that exceed these limits will be discarded.

Timezone

The server side uses Beijing Time (UTC+8).

File System

Your application can create temporary files under /home/leanengine and /tmp. The size limit for all the files created by your application is 1 GB.

caution

Each time you trigger a new deployment for your application, Cloud Engine will create a new container for it. Even though you don’t trigger deployments, Cloud Engine will still perform occasional maintenance operations. This means that your application should not treat the file system provided by Cloud Engine as permanent storage.

If the files created by your application bear relatively larger sizes, we recommend that your application always cleans them up once it finishes using them. Creating more files when there are already more than 1 GB files existing might lead to the Disk quota exceeded error. You can trigger a deployment to quickly clean up all the temporary files.

IP Addresses

Some third-party platforms (like Weixin Open Platform) may require that you provide an IP address whitelist. You can obtain the inbound and outbound IP addresses used by Cloud Engine on Dashboard > LeanEngine > Your group > Settings > Inbound IP and outbound IP.

info

For Cloud Engine applications deployed within Mainland China, CDN will be enabled by default. Depending on the provider we use, the inbound IP addresses might be changed frequently. To get a fixed inbound IP address for your application, consider enabling dedicated IP.

We will do our best to minimize the frequency of changing the inbound and outbound IP addresses, but there remains the possibility for them to get changed. If you encounter any problems with IP addresses, the first thing you can do is look at the IP addresses displayed on the dashboard and see if they have been changed.

To get a fixed inbound IP address for your application, consider enabling dedicated IP.

Troubleshooting

Can I run my Cloud Engine Java project locally without using the CLI?

Once you have configured the environment variables required for running your project on Cloud Engine, you can run your Java project locally with certain commands or using an IDE without using the CLI.

To run a Jetty or JAR project from the command line, first configure the environment variables:

eval "$(lean env)"

Notice that lean env outputs the commands used to configure the environment variables required for the current application. You can use eval to execute these commands. If you’re using Windows, you need to manually configure the environment variables returned by lean env.

If you have a Jetty project, run the following command:

mvn jetty:run

If you have a JAR project, package it with Maven and run the following command:

mvn package
java -jar target/{zipped jar file}

To run the application with Eclipse:

Please first make sure that you have installed the Maven plugin with Eclipse, then import the project into Eclipse as a Maven Project.

After this, right-click on the project under the Package Explorer view:

For a Jetty project, select Run As > Maven build… and set Goals under the Main tab to be jetty:run.
For a JAR project, select Run As > Run Configurations…, select Application, and set Main class: (cn.leancloud.demo.todo.Application for the sample project).

Then add the following environment variables under the Environment tab:

Name	Value
`LEANCLOUD_APP_ENV`	`development`
`LEANCLOUD_APP_ID`	`{{appid}}`
`LEANCLOUD_APP_KEY`	`{{appkey}}`
`LEANCLOUD_APP_MASTER_KEY`	`{{masterkey}}`
`LEANCLOUD_APP_PORT`	`3000`

Once you’ve finished the configuration above, you will be able to run your project by hitting run.

If my project depends on private libraries, can I use them on Cloud Engine?

You can follow the instructions below to use private libraries on Cloud Engine:

Create a directory named libs under the root directory of your project, then copy all the jar files your project depends on into it.
Create a file named leanengine.yaml under the root directory of your project, then customize the install stage (see the example below).
Edit the dependencies in pom.xml and add includeSystemScope into spring-boot-maven-plugin in the same file (see the example below).

Your project structure will look like this:

{root}
|---libs
|       |- yourdependency.jar etc.
|---leanengine.yaml
\---pom.xml

leanengine.yaml will look like this:

install:
  - require:
      - libs
  - { use: "default" }

To add dependencies into pom.xml:

<dependency>
    <groupId>com.sample</groupId>
    <artifactId>sample</artifactId>
    <version>1.0</version>
    <scope>system</scope>
    <systemPath>${project.basedir}/libs/yourdependency.jar</systemPath>
</dependency>

Edit spring-boot-maven-plugin in pom.xml so it looks like this:

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <executable>true</executable>
    <includeSystemScope>true</includeSystemScope>
  </configuration>
</plugin>

Startup Command​

Configure JVM Parameters​

Configure Java Version​

Upload WAR File​

Install Dependencies and Build​

Customize Build Process​

Overriding Command for Execution With run​

Overriding Command for Installing Dependencies With install​

Overriding Command for Building With build​

Build Logs​

System Dependencies​

Health Check​

Cloud Environment​

Custom Domains​

Load Balancer and CDN​

Getting the Client IP Address​

HTTPS Redirect​

CDN Caching​

Environment Variables​

Logs​

Timezone​

File System​

IP Addresses​

Troubleshooting​

Can I run my Cloud Engine Java project locally without using the CLI?​

If my project depends on private libraries, can I use them on Cloud Engine?​

Startup Command

Configure JVM Parameters

Configure Java Version

Upload WAR File

Install Dependencies and Build

Customize Build Process

Overriding Command for Execution With `run`

Overriding Command for Installing Dependencies With `install`

Overriding Command for Building With `build`

Build Logs

System Dependencies

Health Check

Cloud Environment

Custom Domains

Load Balancer and CDN

Getting the Client IP Address

HTTPS Redirect

CDN Caching

Environment Variables

Logs

Timezone

File System

IP Addresses

Troubleshooting

Can I run my Cloud Engine Java project locally without using the CLI?

If my project depends on private libraries, can I use them on Cloud Engine?