Run a C++ app
In this guide we create and deploy a simple C++-based HTTP web server. To run this example, follow these steps:
-
Install the
kraft
CLI tool and a container runtime engine, e.g. Docker. -
Clone the example repository and
cd
into theexamples/http-cpp/
directory:
git clone https://github.com/kraftcloud/examplescd examples/http-cpp/
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 tokenexport UKC_TOKEN=token# Set metro to Frankfurt, DEexport 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-cpp-jzbuo ├────────── uuid: b8e015fd-d006-49d5-849e-3fd497c9159a ├───────── state: running ├─────────── url: https://throbbing-wave-grxjih4t.fra0.kraft.host ├───────── image: http-cpp@sha256:a58873987104b52c13b79168a2e2f1a81876ba6efacd6dbc98e996afe5c09699 ├───── boot time: 15.61 ms ├──────── memory: 128 MiB ├─────── service: throbbing-wave-grxjih4t ├── private fqdn: http-cpp-jzbuo.internal ├──── private ip: 172.16.6.5 └────────── args: /http_server
In this case, the instance name is http-cpp-jzbuo
and the URL is https://throbbing-wave-grxjih4t.fra0.kraft.host
.
They are different for each run.
Use curl
to query the Unikraft Cloud instance of the C++ HTTP web server:
curl https://throbbing-wave-grxjih4t.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 TIMEhttp-cpp-jzbuo throbbing-wave-grxjih4t.fra0.kraft.host running 1 minute ago http-cpp@sha256:a58873987104b52c13b79168a2e2f1a81876ba6efac... 128 MiB /http_server 15614us
When done, you can remove the instance:
kraft cloud instance remove http-cpp-jzbuo
Customize your Application
To customize the application, update the files in the repository, listed below:
http_server.cpp
: the actual C++ HTTP serverKraftfile
: the Unikraft Cloud specificationDockerfile
: the Docker-specified application filesystem
/* SPDX-License-Identifier: BSD-3-Clause *//** Copyright (c) 2023, Unikraft GmbH and the Unikraft Authors.*/
#include <iostream>#include <cstring>#include <sys/socket.h>#include <arpa/inet.h>#include <unistd.h>#include <errno.h>
#define LISTEN_PORT 8080
static std::string reply = "HTTP/1.1 200 OK\r\n" \ "Content-Type: text/html\r\n" \ "Content-Length: 14\r\n" \ "Connection: close\r\n" \ "\r\n" \ "Hello, World!\n";
#define BUFLEN 2048static char recvbuf[BUFLEN];
int main(int argc __attribute__((unused)), char *argv[] __attribute__((unused))){int rc = 0;int srv, client;ssize_t n;struct sockaddr_in srv_addr;
srv = socket(AF_INET, SOCK_STREAM, 0);if (srv < 0) { std::cerr << "Failed to create socket: " << errno << std::endl; goto out;}
srv_addr.sin_family = AF_INET;srv_addr.sin_addr.s_addr = INADDR_ANY;srv_addr.sin_port = htons(LISTEN_PORT);
rc = bind(srv, (struct sockaddr *) &srv_addr, sizeof(srv_addr));if (rc < 0) { std::cerr << "Failed to bind socket: " << errno << std::endl; goto out;}
/* Accept one simultaneous connection */rc = listen(srv, 1);if (rc < 0) { std::cerr << "Failed to listen on socket: " << errno << std::endl; goto out;}
std::cout << "Listening on port " << LISTEN_PORT << std::endl;while (1) { client = accept(srv, NULL, 0); if (client < 0) { std::cerr << "Failed to accept incoming connection: " << errno << std::endl; goto out; }
/* Receive some bytes (ignore errors) */ read(client, recvbuf, BUFLEN);
/* Send reply */ n = write(client, reply.c_str(), reply.length()); if (n < 0) std::cerr << "Failed to send reply" << std::endl; else std::cout << "Sent a reply" << std::endl;
/* Close connection */ close(client);}
out:return rc;}
spec: v0.6
runtime: base:latest
rootfs: ./Dockerfile
cmd: ["/http_server"]
FROM --platform=linux/x86_64 gcc:13.2.0-bookworm AS build
WORKDIR /src
COPY ./http_server.cpp /src/http_server.cpp
RUN set -xe; \g++ \-Wall -Wextra \-fPIC -pie \-o /http_server http_server.cpp
FROM scratch
# System / C++ librariesCOPY --from=build /lib/x86_64-linux-gnu/libc.so.6 /lib/x86_64-linux-gnu/COPY --from=build /lib/x86_64-linux-gnu/libm.so.6 /lib/x86_64-linux-gnu/libm.so.6COPY --from=build /usr/local/lib64/libgcc_s.so.1 /usr/local/lib64/libgcc_s.so.1COPY --from=build /usr/local/lib64/libstdc++.so.6 /usr/local/lib64/libstdc++.so.6COPY --from=build /lib64/ld-linux-x86-64.so.2 /lib64/ld-linux-x86-64.so.2COPY --from=build /etc/ld.so.cache /etc/ld.so.cache
# C++ HTTP serverCOPY --from=build /http_server /http_server
Lines in the Kraftfile
have the following roles:
-
spec: v0.6
: The currentKraftfile
specification version is0.6
. -
runtime: base
: The Unikraft runtime kernel to use is its base one. -
rootfs: ./Dockerfile
: Build the application root filesystem using theDockerfile
. -
cmd: ["/http_server"]
: Use/http_server
as the starting command of the instance.
Lines in the Dockerfile
have the following roles:
-
FROM --platform=linux/x86_64 gcc:13.2.0-bookworm AS build
: Build the filesystem from thebookworm gcc
container image, to create a base image. -
COPY ./http_server.cpp /src/http_server.cpp
: Copy the server implementation file (http_server.cpp
) in the Docker filesystem (in/src/http_server.cpp
).
The following options are available for customizing the application:
-
If only updating the implementation in the
http_server.cpp
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 theDockerfile
. -
If a new C++ source files is added, update the
cmd
line in theKraftfile
and replacehttp_server.cpp
to run that file when creating the instance. -
More extensive changes may require expanding the
Dockerfile
with additionalDockerfile
commands.
Learn More
Use the --help
option for detailed information on using Unikraft Cloud:
kraft cloud --help
Or visit the CLI Reference.