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Run a Lua app

In this guide we create and deploy a simple Lua-based HTTP web server. To run this example, follow these steps:

  1. Install the kraft CLI tool and a container runtime engine, e.g. Docker.

  2. Clone the examples repository and cd into the http-lua5.1 directory.

Terminal window
git clone
cd examples/http-lua5.1/

Make sure to log into KraftCloud by setting your token and a metro close to you. We use fra0 (Frankfurt, 🇩🇪) in this guide:

Terminal window
# Set KraftCloud access token
# Set metro to Frankfurt, DE

When done, invoke the following command to deploy this application on KraftCloud:

Terminal window
kraft cloud deploy -p 443:8080 .

The output shows the instance URL and other details:

Terminal window
[] Deployed successfully!
────────── name: http-lua51-ma2i9
────────── uuid: e7389eee-9808-4152-b2ec-1f3c0541fd05
───────── state: running
─────────── url:
───────── image: http-lua51@sha256:278cb8b14f9faf9c2702dddd8bfb6124912d82c11b4a2c6590b6e32fc4049472
───── boot time: 15.09 ms
──────── memory: 128 MiB
service group: young-night-5fpf0jj8
── private fqdn: http-lua51-ma2i9.internal
──── private ip:
────────── args: /usr/bin/lua /http_server.lua

In this case, the instance name is http-lua51-ma2i9 and the URL is They are different for each run.

Use curl to query the KraftCloud instance of the Lua-based HTTP web server:

Terminal window
Hello, World!

At any point in time, you can list information about the instance:

Terminal window
kraft cloud instance list
http-lua51-ma2i9 running 1 minute ago 128 MiB /usr/bin/lua /http_server.lua 15094us

When done, you can remove the instance:

Terminal window
kraft cloud instance remove http-lua51-ma2i9

Customize your Application

To customize the application, update the files in the repository, listed below:

  • http_server.lua: the actual Lua HTTP server
  • Kraftfile: the KraftCloud specification
  • Dockerfile: the Docker-specified application filesystem
#!/usr/bin/env lua
A simple HTTP server
If a request is not a HEAD method, then reply with "Hello world!"
Usage: lua examples/server_hello.lua [<port>]
local port = arg[1] or 8080
local http_server = require "http.server"
local http_headers = require "http.headers"
local function reply(myserver, stream) -- luacheck: ignore 212
-- Read in headers
local req_headers = assert(stream:get_headers())
local req_method = req_headers:get ":method"
-- Log request to stdout
assert(io.stdout:write(string.format('[%s] "%s %s HTTP/%g" "%s" "%s"\n',"%d/%b/%Y:%H:%M:%S %z"),
req_method or "",
req_headers:get(":path") or "",
req_headers:get("referer") or "-",
req_headers:get("user-agent") or "-"
-- Build response headers
local res_headers =
res_headers:append(":status", "200")
res_headers:append("content-type", "text/plain")
-- Send headers to client; end the stream immediately if this was a HEAD request
assert(stream:write_headers(res_headers, req_method == "HEAD"))
if req_method ~= "HEAD" then
-- Send body, ending the stream
assert(stream:write_chunk("Hello, World!\n", true))
local myserver = assert(http_server.listen {
host = "";
port = port;
onstream = reply;
onerror = function(myserver, context, op, err, errno) -- luacheck: ignore 212
local msg = op .. " on " .. tostring(context) .. " failed"
if err then
msg = msg .. ": " .. tostring(err)
assert(io.stderr:write(msg, "\n"))
-- Manually call :listen() so that we are bound before calling :localname()
local bound_port = select(3, myserver:localname())
assert(io.stderr:write(string.format("Now listening on port %d\n", bound_port)))
-- Start the main server loop

The following options are available for customizing the application:

  • If only updating the implementation in the http_server.lua source file, no other change is required.

  • If new files are added, these have to be copied in the application filesystem, using the COPY command in the Dockerfile.

  • If a new Lua source files is added, update the cmd line in the Kraftfile and replace http_server.lua to run that file when creating the instance.

  • More extensive changes may require expanding the Dockerfile with additional Dockerfile commands.

Learn More

Use the --help option for detailed information on using KraftCloud:

Terminal window
kraft cloud --help

Or visit the CLI Reference.