eCAL in Docker#

Here we will show how to deploy eCAL into a docker container, and how to use its image from other containers.

Important

This will work with eCAL 5.10 and up. Older eCAL versions will lack Shared Memory communication when being run in a docker container.

Prerequisite#

Install Docker as described in the Docker installation documentation
See also

If you have problems regarding to the installation, check these links:
- Docker package not found
- Docker installation failed
Optional: If you want your docker container to talk to eCAL Nodes on other machines: Set up you multicast routes on the host.
Optional: If you want to use eCAL on your host to subscribe to data from your docker containers: Install eCAL on the host.

Getting Started#

In this tutorial we are going to create:

A general purpose eCAL Docker container
A publisher container with a custom Hello World Publisher
A subscriber container receiving the Hello World data.

The file hierarchy that we are going to follow:

 ecal_in_docker
├─  docker-compose.yaml
|
├─  ecal_runtime_container
|  └─  Dockerfile
|
├─  pub_container
|  ├─  Dockerfile
|  ├─  CMakeLists.txt
|  └─  main.cpp
|
└─  sub_container
   ├─  Dockerfile
   ├─  CMakeLists.txt
   └─  main.cpp

eCAL runtime container#

Create the file ecal_runtime_container/Dockerfile and paste the following installation commands:

# Base image:
FROM ubuntu:focal

# Install eCAL from PPA:
RUN apt-get update && \
	apt-get install -y software-properties-common && \
	rm -rf /var/lib/apt/lists/*
RUN add-apt-repository ppa:ecal/ecal-latest
RUN apt-get install -y ecal

# Install dependencies for compiling the hello world examples.
# You can omit this, if you don't want to build applications in the container.
RUN apt-get install -y cmake g++ libprotobuf-dev protobuf-compiler

# Set network_enabled = true in ecal.ini.
# You can omit this, if you only need local communication.
RUN awk -F"=" '/^network_enabled/{$2="= true"}1' /etc/ecal/ecal.ini > /etc/ecal/ecal.tmp && \
	rm /etc/ecal/ecal.ini && \
	mv /etc/ecal/ecal.tmp /etc/ecal/ecal.ini 

# Print the eCAL config
RUN ecal_config

Build the image:

cd ecal_in_docker
sudo docker build . --rm -t ecal-runtime

Test the image
```
sudo docker run --rm -it --ipc=host --pid=host --network=host ecal-runtime
```
At this point you are in the docker container. You can exit it with exit. If you run ecal_sample_person_snd in the docker container and have an eCAL installation on your host, you can subscribe to the data via the eCAL Monitor or ecal_sample_person_rec.
Note
- --ipc=host will enable Shared Memory communication with your host system and other docker containers that are started with the same parameter. This is important for local communication.
- --network=host will share the host’s network. This is important for network communcation with other machines. It is also important for local shared memory communication, as it affects the hostname of the container. The hostname is used to determine whether an eCAL topic is avaialble via shared memory.
- --pid=host will share the Process-ID range with the host. Otherwise processes from different containers may get the same Process ID, which will prevent communication between those two processes.

Publisher container#

The publisher container will be built on top of the ecal-runtime container. It will contain the Hello World Sample from the Getting Started Section.

Create a file pub_container/Dockerfile and paste the following content:

#ecal base image:
FROM ecal-runtime

WORKDIR /src/pub

COPY CMakeLists.txt main.cpp ./
RUN cmake . && make
CMD ./hello_world_snd

Create publisher source code: pub_container/main.cpp

#include <ecal/ecal.h>
#include <ecal/msg/string/publisher.h>

#include <iostream>
#include <thread>

int main(int argc, char** argv)
{
  // Initialize eCAL. The name of our Process will be "Hello World Publisher"
  eCAL::Initialize(argc, argv, "Hello World Publisher");

  // Create a String Publisher that publishes on the topic "hello_world_topic"
  eCAL::string::CPublisher<std::string> publisher("hello_world_topic");

  // Create a counter, so something changes in our message
  int counter = 0;

  // Infinite loop (using eCAL::Ok() will enable us to gracefully shutdown the
  // Process from another application)
  while (eCAL::Ok())
  {
    // Create a message with a counter an publish it to the topic
    std::string message = "Hello World " + std::to_string(++counter);
    std::cout << "Sending message: " << message << std::endl;
    publisher.Send(message);

    // Sleep 500 ms
    std::this_thread::sleep_for(std::chrono::milliseconds(500));
  }

  // finalize eCAL API
  eCAL::Finalize();
}

Create file pub_container/CMakeLists.txt

cmake_minimum_required(VERSION 3.0)
set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ON)

project(hello_world_snd)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(eCAL REQUIRED)

set(source_files
  main.cpp
)

add_executable(${PROJECT_NAME} ${source_files})

target_link_libraries(${PROJECT_NAME}
  eCAL::core
)

Build the image:

cd pub_container
sudo docker build . --rm -t ecal-publisher:1.0.0

Subscriber container#

The subscriber container will also be based on the ecal-runtime container and contain the Hello World Sample from the Getting Started Section.

Create a file: sub_container/Dockerfile

#ecal base image:
FROM ecal-runtime

WORKDIR /src/sub

COPY CMakeLists.txt main.cpp ./
RUN cmake . && make
CMD ./hello_world_rec

Create subscriber source code: sub_container/main.cpp

#include <ecal/ecal.h>
#include <ecal/msg/string/subscriber.h>

#include <iostream>
#include <thread>

// Callback for receiving messages
void HelloWorldCallback(const std::string& message)
{
  std::cout << "Received Message: " << message << std::endl;
}

int main(int argc, char** argv)
{
  // Initialize eCAL
  eCAL::Initialize(argc, argv, "Hello World Subscriber");

  // Create a subscriber that listenes on the "hello_world_topic"
  eCAL::string::CSubscriber<std::string> subscriber("hello_world_topic");

  // Set the Callback
  subscriber.AddReceiveCallback(std::bind(&HelloWorldCallback, std::placeholders::_2));

  // Just don't exit
  while (eCAL::Ok())
  {
    std::this_thread::sleep_for(std::chrono::milliseconds(500));
  }

  // finalize eCAL API
  eCAL::Finalize();
}

Create file sub_container/CMakeLists.txt

cmake_minimum_required(VERSION 3.0)
set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ON)

project(hello_world_rec)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(eCAL REQUIRED)

set(source_files
  main.cpp
)

add_executable(${PROJECT_NAME} ${source_files})

target_link_libraries(${PROJECT_NAME}
  eCAL::core
)

Build the image:

cd sub_container
sudo docker build . --rm -t ecal-subscriber:1.0.0

Run the docker containers#

You can run the publisher and subscriber images manually with docker run.

sudo docker run --rm -it --ipc=host --network=host --pid=host ecal-subscriber:1.0.0
sudo docker run --rm -it --ipc=host --network=host --pid=host ecal-publisher:1.0.0

You can also use the docker-compose file to manage multiple containers.

In the parent folder create file docker-compose.yaml and paste the following content:

version: "3"

services:
    subscriber:
        build: ./sub_container
        image: ecal-subscriber:1.0.0
        container_name: ecal-subscriber
        network_mode: host
        ipc: host
        pid: host
    publisher:
        build: ./pub_container
        image: ecal-publisher:1.0.0
        container_name: ecal-publisher
        network_mode: host
        ipc: host
        pid: host

You can now use that docker-compose to build/run the publisher and subscriber containers:
```
sudo docker-compose build
sudo docker-compose up
```

eCAL in Docker

Contents

eCAL in Docker#

Prerequisite#

Getting Started#

eCAL runtime container#

Publisher container#

Subscriber container#

Run the docker containers#