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 examples/http-lua5.1/ directory:

git clone https://github.com/kraftcloud/examples
cd examples/http-lua5.1/

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

# Set Unikraft Cloud access token
export UKC_TOKEN=token
# Set metro to Frankfurt, DE
export UKC_METRO=fra0

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

kraft cloud deploy -p 443:8080 .

The output shows the instance URL and other details:

[●] Deployed successfully!
 │
 ├────────── name: http-lua51-ma2i9
 ├────────── uuid: e7389eee-9808-4152-b2ec-1f3c0541fd05
 ├───────── state: running
 ├─────────── url: https://young-night-5fpf0jj8.fra0.kraft.host
 ├───────── image: http-lua51@sha256:278cb8b14f9faf9c2702dddd8bfb6124912d82c11b4a2c6590b6e32fc4049472
 ├───── boot time: 15.09 ms
 ├──────── memory: 128 MiB
 ├─────── service: young-night-5fpf0jj8
 ├── private fqdn: http-lua51-ma2i9.internal
 ├──── private ip: 172.16.3.3
 └────────── args: /usr/bin/lua /http_server.lua

In this case, the instance name is http-lua51-ma2i9 and the URL is https://young-night-5fpf0jj8.fra0.kraft.host. They are different for each run.

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

curl https://young-night-5fpf0jj8.fra0.kraft.host

Hello, World!

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

kraft cloud instance list

NAME              FQDN                                  STATE    CREATED AT    IMAGE                                    MEMORY   ARGS                           BOOT TIME
http-lua51-ma2i9  young-night-5fpf0jj8.fra0.kraft.host  running  1 minute ago  http-lua51@sha256:278cb8b14f9faf9c27...  128 MiB  /usr/bin/lua /http_server.lua  15094us

When done, you can remove the instance:

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 Unikraft Cloud specification
• Dockerfile: the Docker-specified application filesystem

http_server.lua

#!/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>]
]]

-- https://github.com/daurnimator/lua-http/blob/master/examples/server_hello.lua
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',
                os.date("%d/%b/%Y:%H:%M:%S %z"),
                req_method or "",
                req_headers:get(":path") or "",
                stream.connection.version,
                req_headers:get("referer") or "-",
                req_headers:get("user-agent") or "-"
        )))

        -- Build response headers
        local res_headers = http_headers.new()
        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))
        end
end

local myserver = assert(http_server.listen {
        host = "0.0.0.0";
        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)
                end
                assert(io.stderr:write(msg, "\n"))
        end;
})

-- Manually call :listen() so that we are bound before calling :localname()
assert(myserver:listen())
do
        local bound_port = select(3, myserver:localname())
        assert(io.stderr:write(string.format("Now listening on port %d\n", bound_port)))
end
-- Start the main server loop
assert(myserver:loop())

Kraftfile

spec: v0.6

runtime: lua:5.1

rootfs: ./Dockerfile

cmd: ["/usr/bin/lua", "/http_server.lua"]

Dockerfile

FROM scratch

# Lua server
COPY ./http_server.lua /http_server.lua

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 Unikraft Cloud:

kraft cloud --help

Or visit the CLI Reference.