This guide describes how to create a FastEdge app. Check out our FastEdge overview article to learn more about the product. You can create a FastEdge app in two ways: from a custom binary file using JavaScript SDK or Rust as well as from a preconfigured template. If you chose the latter option, skip Stage 1.

​
Stage 1. Create a Wasm binary file

To get started, create a .wasm file that you will later upload to the Gcore Customer Portal.

​
Step 1. Set up the environment

1. Install the Rust compiler and cargo (package manager):
curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
2. Add the Wasm compilation target to Rust compiler:
rustup target add wasm32-wasip1

​
Step 2. Prepare directory structure and a configuration file

1. Initialize the directory structure:
cargo new myapp --lib
2. Create a directory:
mkdir myapp/.cargo
3. Set the Wasm compilation target for the project by creating a config file myapp/.cargo/config.toml with the following content:
[build]
target = "wasm32-wasip1"
4. Create the project manifest file myapp/Cargo.toml with the following content:
[package]
name = "myapp"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib"]

[dependencies]
fastedge = "0.2"

​
Step 3. Create a source

In this example, we’ll create a simple app that responds with “HTTP 200” and the text “Hello world!” in the response’s body.Create a main source file src/lib.rs with the following content:
use fastedge::{
  body::Body,
  http::{Request, Response, StatusCode, Error},
};

#[fastedge::http]
fn main(_req: Request<Body>) -> Result<Response<Body>, Error> {
  Response::builder()
    .status(StatusCode::OK)
    .body(Body::from("Hello world!\n"))
  }

​
Step 4. Compile a Wasm file

Produce the Wasm binary:
cargo build --release
The resulting Wasm code will be written to the myapp/target/wasm32-wasip1/release/myapp.wasm file.

​
Stage 2. Deploy an application

For detailed steps on how to deploy a FastEdge app, refer to the relevant sections below:
  • In the Customer Portal. Follow the instructions if you created a custom Wasm using either the Rust or Javascript SDK, or if you want to create a FastEdge app from a preconfigured template.
  • Via command line: Follow the instructions if you want to deploy a custom Wasm using cURL and our API.

​
In the customer portal

1. In the Gcore Customer Portal, navigate to FastEdge > HTTP Applications.2. In the top-right corner of the screen, click Create new application.
Create an HTTP app button highlighted
3. Click Upload binary.
Add raw binary dialog
4. Choose your custom binary file.
Add raw binary dialog
5. If you add multiple files, click Save binary to confirm and upload the selected files.6. Enter a name for your application and provide a description if needed.7. (Optional) Click + Add response headers to add fixed headers to the responses. For example, you may include CORS (cross-origin resource sharing) headers in each response to ensure secure communication between origins.8. (Optional) If you want to customize the behavior of your application, click + Add environment variables and enter your data as key-value pairs.If you’re adding sensitive information or want to ensure that any data in the app’s configuration remains secure, encrypt the variables. Click Encrypt next to the value you want to secure:
Encrypt variable button highlighted
The provided value will be replaced with the Encrypted Value text, and the Revert button will appear next to encrypted value. This button allows you to restore the original version if needed. Note that once you save the configuration, you won’t be able to view the original unencrypted value.
Encrypted variable
We store all encrypted variables in a separate table in the database to protect your information from potential security breaches or unauthorized access.
WarningYou won’t be able to update the encrypted variable after creating the application. To change the value, delete the existing variable and add a new encrypted variable with the updated value.
9. Check all the settings. If everything is configured correctly, click Save and deploy.Your application has been successfully deployed.
A page with a link to an app and its configuration
You can now test its configuration and adjust it as described in the following steps.

​
Via command line

1. Upload the Wasm binary to our edge servers by running the following API request from the repo’s root directory. Insert your permanent API token instead of the api_key: 
curl -X 'POST' 
  'https://api.gcore.com/fastedge/v1/binaries/raw' \ 
  -H 'accept: application/json' 
  -H 'Authorization: APIKey api_key' 
  -H 'Content-Type: application/octet-stream' 
  --data-binary '@./dist/main.wasm'
In the response, you will receive the ID of the uploaded binary (<binary_id>). Make sure to save it, as it will be used in the following step. 2. Create the app by running the following API request: 
curl -X 'POST' 
  'https://api.gcore.com/fastedge/v1/apps' 
  -H 'name: app_name' 
  -H 'accept: application/json' 
  -H 'client_id: 0' 
  -H 'Authorization: APIKey api_key' 
  -H 'Content-Type: application/json' 
  -d '{
    "binary": binary_id,
    "plan": "beta",
    "status": 1
}'
Where:
  • app_name is the unique name of your app.
  • api_key is your permanent API token.
  • binary_id is the ID of your uploaded Wasm binary.

​
Stage 3. Test an application

You can test the application after its deployment by clicking the application link on the deployment confirmation screen:
A page with a link to an app and its configuration
Additionally, you can inspect and adjust the configuration in the Customer Portal on the Dashboards page:1. In the Gcore Customer Portal, navigate to FastEdge > Dashboard.
Metrics tab with the list of FastEdge apps
2. Find the app you want to test and click its name to open it.3. Click the app link next to the app status to view the response.
A page with a link to an app and its configuration
For example, the response for the application configured in Stage 1 will be “Hello world!”.

​
Stage 4 (Optional). Add more functionality

You can add more functionality to your app. For example, instead of printing “Hello world!”, the app can print all request headers and set a custom response header from the environment settings. Let’s see how to do that.

​
Step 1. Change the source

To print all request headers and develop a custom response header, replace the current content of the myapp/src/lib.rs file with the following:
use fastedge::{
    body::Body,
    http::{Request, Response, StatusCode, Error},
};
use std::env;

#[fastedge::http]
fn main(req: Request<Body>) -> Result<Response<Body>, Error> {
    // print headers
    let mut body: String = "".to_string();
    for (h, v) in req.headers() {
        body.push_str(h.as_str());
        body.push_str(": ");
        match v.to_str() {
            Err(_) => body.push_str("not a valid text"),
            Ok(a) => body.push_str(a),
        }
        body.push_str("\n");
    }

    // get value for custom header from the env var
    let value = match env::var("CUSTOM_HEADER").ok() {
        None => return Response::builder()
                    .status(StatusCode::INTERNAL_SERVER_ERROR)
                    .body(Body::from("App misconfigured\n")),
        Some(val) => val
    };

    // build response with body and custom header
    Response::builder()
        .status(StatusCode::OK)
        .header("Custom-Header", value)
        .body(Body::from(body))
}
InfoThe headers listed in the following step are passed to the FastEdge application, which uses the header content for functionalities like geolocation-aware redirects.

​
Step 2. Compile and upload the binary file

Update the application on the edge servers:1. Compile a new Wasm file as described in step 4.2. Upload it to the Gcore Customer Portal as a custom binary file.When you open the app, you’ll see all request headers from the environment settings. It will be similar to the following output:
HTTP/2 200
server: nginx
date: Thu, 19 Oct 2023 22:17:46 GMT
content-length: 616
custom-header: foo 
access-control-allow-origin: *
cache-control: no-store
x-id: ed-hw-edge-preprod-gc39
cache: MISS
accept-ranges: bytes 
dc: ed 
geoip-asn: 7922 
geoip-lat: 37.75580
geoip-long: -121.95270
geoip-reg: CA
geoip-city: San Ramon
geoip-continent: NA
geoip-country-name: United States
geoip-country-code: US
server_addr: 92.223.112.26 
server_name: mistake-globe-6396.fastedge.gcore.dev 
connection: upgrade
x-real-ip: 1.2.3.4 
x-forwarded-for: 1.2.3.4 
host: fastedge.gcore.dev
x-forwarded-proto: https
user-agent: curl/7.88.1
accept: */*
cdn-loop: nb1d2; c=11
pop-long: 6.1294
pop-lat: 49.6113
pop-reg: LU
pop-continent: EU
pop-city: Luxembourg
pop-country-code: LU
pop-country-name: Luxembourg

​
Troubleshoot an application

If you’re having issues with your FastEdge application, the following sections offer helpful tips and troubleshooting suggestions.

​
HTTP status codes

If your application is correctly configured and works as expected, FastEdge will return the expected status code, such as “200 OK.” However, in some exceptional situations, you might get the following status codes. Check the descriptions to understand the root cause.
Status codeDescription
530Internal FastEdge error.
531Application has exceeded the allowed memory limit.
532Application has timed out.
533Application has crashed.