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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​

You can override the default behavior by specifying startup commands (run), dependency installation commands (install), and build commands (build) in leanengine.yaml:

leanengine.yaml
run: echo 'run another command'
install:
  - {use: 'default'}
  - echo 'install additional dependencies here'
build:
  - echo 'overwrite default build command here'

See Reference: leanengine.yaml for more information. Below are a few examples:

Upload Jar Without Building on the Server​

leanengine.yaml
runtime: java
install: []
build: []
run: java -jar your-package.jar

Here we have specified that we are using the Java Runtime Environment. We have skipped the dependency installation and build steps by leaving them empty. We also specified the run command (run your-package.jar in the root directory).

System Dependencies​

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

leanengine.yaml
systemDependencies:
  - imagemagick

See Reference: leanengine.yaml for a complete list of supported system dependencies.

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.

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 > Manage deployment > 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 > Manage deployment > 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).
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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 nameDescription
LEANCLOUD_APP_IDThe App ID of the current application.
LEANCLOUD_APP_KEYThe App Key of the current application.
LEANCLOUD_APP_MASTER_KEYThe Master Key of the current application.
LEANCLOUD_APP_ENVThe 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_PORTThe port opened up for your application. Your application has to listen on this port in order for users to access your service.
LEANCLOUD_API_SERVERThe 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_GROUPThe group the instance is located at.
LEANCLOUD_REGIONThe region the application is running in. It will be CN for Mainland China and US for the United States.
LEANCLOUD_VERSION_TAGThe 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_.

You can also set up custom environment variables on the dashboard to store configurations.

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 > Manage deployment > 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:

NameValue
LEANCLOUD_APP_ENVdevelopment
LEANCLOUD_APP_ID{{appid}}
LEANCLOUD_APP_KEY{{appkey}}
LEANCLOUD_APP_MASTER_KEY{{masterkey}}
LEANCLOUD_APP_PORT3000

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:

  1. Create a directory named libs under the root directory of your project, then copy all the jar files your project depends on into it.
  2. Create a file named leanengine.yaml under the root directory of your project, then customize the install stage (see the example below).
  3. 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>