I have implemented the LAMP stack for a 3rd party forum application on its own dedicated virtual server. One of my aims here was to use a composed docker project (under Git) to encapsulate the application fully. I wanted to keep this as simple to understand as possible for the other sysAdmins supporting the forum, so this really ruled out using S6 etc., and this in turn meant that I had to stick to the standard of one container per daemon service using the docker runtime to do implement the daemon functionality.
I had one particular design challenge that doesn't seem to be addressed cleanly through the Docker runtime system, and that is I need to run periodic housekeeping activities that need to interact across various docker containers, for example:
The forum application requires a per-minute PHP housekeeping task to be run using php-cli, and I only have php-cli and php-fpm (which runs as the foreground deamon process) installed in the php container.
Letsencrypt certificate renewal need a weekly certbot script to be run in the apache container's file hierarchy.
I use conventional /var/log based logging for high-volume Apache access logs as these generate Gb access files that I want to retain for ~7 days in the event of needing to do hack analysis, but that are otherwise ignored.
Yes I could use the hosts crontab to run docker exec commands but this involves exposing application internals to the host system and IMO this is breaking one of my design rules. What follows is my approach to address this. My Q is really to ask for comments and better alternative approaches, and if not then this can perhaps serve as a template for others searching for an approach to this challenge.
All of my containers contain two special to container scripts: docker-entrypoint.sh which is a well documented convention; docker-service-callback.sh which is the action mechanism to implement the tasking system.
I have one application agnostic host service systemctl: docker-callback-reader.service which uses this bash script, docker-callback-reader. This services requests on a /run pipe that is volume-mapped into any container that need to request such event processes.
In practice I have only one such housekeeping container see here that implements Alpine crond and runs all of the cron-based events. So for example the following entry does the per-minute PHP tasking call:
- * * * * echo ${VHOST} php task >/run/host-callback.pipe
In this case the env variable VHOST identifies the relevant docker stack, as I can have multiple instances (forum and test) running on the server; the next parameter (php in this case) identifies the destination service container; the final parameter (task) plus any optional parameters are passed as arguments to a docker exec of php containers docker-service-callback.sh and magic happens as required.
I feel that the strengths of the system are that:
Everything is suitably encapsulated. The host knows nothing of the internals of the app other than any receiving container must have a docker-service-callback.sh on its execution path. The details of each request are implemented internally in the executing container, and are hidden from the tasking container.
The whole implementation is simple, robust and has minimal overhead.
Anyone is free to browse my Git repo and cherry-pick whatever of this they wish.
Comments?
I have a couple of questions related to the usage of Docker in a development phase.
I am going to propose three different scenarios of how I think Docker could be used in a development environment. Let's imagine that we are creating a REST API in Java and Spring Boot. For this I will need a MySQL database.
The first scenario is to have a docker-compose for development with the MySQL container and a production docker-compose with MySQL and the Java application (jar) in another container. To develop I launch the docker-compose-dev.yml to start only the database. The application is launched and debugged using the IDE, for example, IntelliJ Idea. Any changes made to the code, the IDE will recognize and relaunch the application by applying the changes.
The second scenario is to have, for both the development and production environment, a docker-compose with the database and application containers. That way, every time I make a change in the code, I have to rebuild the image so that the changes are loaded in the image and the containers are lauched again. This scenario may be the most typical and used for development with Docker, but it seems very slow due to the need to rebuild the image every time there is a change.
The third scenario consists of the mixture of the previous two. Two docker-compose. The development docker-compose contains both containers, but with mechanisms that allow a live reload of the application, mapping volumes and using, for example, Spring Dev Tools. In this way, the containers are launched and, in case of any change in the files, the application container will detect that there is a change and will be relaunched. For production, a docker-compose would be created simply with both containers, but without the functionality of live reload. This would be the ideal scenario, in my opinion, but I think it is very dependent on the technologies used since not all allow live reload.
The questions are as follows.
Which of these scenarios is the most typical when using Docker for phase?
Is scenario 1 well raised? That is, dockerize only external services, such as databases, queues, etc. and perform the development and debugging of the application with the IDE without using Docker for it.
The doubts and the scenarios that I raise came up after I raised the problem that scenario 2 has. With each change in the code, having to rebuild the image and start the containers again is a significant waste of time. In short, a question would be: How to avoid this?
Thanks in advance for your time.
NOTE: It may be a question subject to opinion, but it would be nice to know how developers usually deal with these problems.
Disclaimer: this is my own opinion on the subject as asked by Mr. Mars. Even though I did my best to back my answer with actual sources, it's mostly based on my own experience and a bit of common sense
Which of these scenarios is the most typical when using Docker for development?
I have seen all 3 scenarios iin several projects, each of them with their advantages and drawbacks. However I think scenario 3 with a Docker Compose allowing for dynamic code reload is the most advantageous in term of flexibility and consistency:
Dev and Prod Docker Compose are close matches, meaning Dev environment is as close as possible to Prod environment
You do not have to rebuild the image constantly when developping, but it's easy to do when you need to
Lots of technologies support such scenario, such as Spring Dev Tools as you mentionned, but also Python Flask, etc.
You can easily leverage Docker Compose extends a.k.a configuration sharing mechanism (also possible with scenario 2)
Is scenario 1 well raised? That is, dockerize only external services, such as databases, queues, etc. and perform the development and debugging of the application with the IDE without using Docker for it.
Scenario 1 is quite common, but the IDE environment would probably be different than the one from the Docker container (and it would be difficult to maintain a match of version for each libs, dependencies, etc. from IDE environment to Docker environment). It would also probably require to go through an intermediate step between Dev and Production to actually test the Docker image built after Dev is working before going to Production.
In my own experience doing this is great when you do not want to deal too much with Docker when actually doing dev and/or the language or technology you use is not adapted for dynamic reload as described in scenario 3. But in the end it only adds a drift between your environments and more complexity between Dev and Prod deployment method.
having to rebuild the image and start the containers again is a significant waste of time. In short, a question would be: How to avoid this?
Beside the scenarios you describe, you have ways to decently (even drastically) reduce image build time by leveraging Docker build cache and designing your Dockerfile. For example, a Python application would typically copy code as the last (or almost last) step of the build to avoid invalidating the cache, and for Java app it would be possible to split code so as to avoid compiling the entire application everytime a bit of code changes - that would depend on your actual setup.
I personally use a workflow roughly matching scenario 3 such as:
a docker-compose.yml file corresponding to my Production environment
a docker-compose.dev.yml which will override some aspect of my main Docker Compose file such as mouting code from my machine, adding dev specific flags to commands, etc. - it would be run such as
docker-compose -f docker-compose.yml -f docker-compose.dev.yml
but it would also be possible to have a docker-compose.override.yml as Docker Compose uses by default for override
in some situation I would have to use other overrides for specific situations such as docker-compose.ci.yml on my CI, but usually the main Docker Compose file is enough to describe my Prod environment (and if that's not the case, docker-compose.prod.yml does the trick)
I've seen them all used in different scenarios. There are some gotchas to avoid:
Applications inside of a container shouldn't depend on something running outside of a container on the host. So all of your dependencies should be containerized first.
File permissions with host volumes can be complicated depending on your version of docker. Some of the newer Docker Desktop installs automatically handle uid mappings, but if you develop directly on Linux you'll need to ensure the containers run as the same uid as your host user.
Avoid making changing inside the container if that isn't mapped into a host volume, since those changes will be lost when the container is recreated.
Looking at each of the options, here's my assessment of each:
Containerizing just the DB: This works well when developers already have a development environment for the language of choice, and there's no risk of external dependencies creeping in, e.g. a developer upgrading their JDK install to a newer version than the image is built with. It follows the idea of containerizing the dependencies first, while also giving developers the familiar IDE integration with their application.
Rebuilding the Image for Every Change: This tends to be the least ideal for developer workflow, but the quickest to implement when you're not familiar with the tooling. I'll give a 4th option that I consider an improvement to this.
Everything in a container, volume mounts, and live reloading: This is the most complicated to implement, and requires the language itself to support things like live reloading. However, when they do, it is nearly seamless for the developers and gets them up to speed on a new project quickly without needing to install any other tooling to get started.
Rebuild the app in the container with volume mounts: This is a halfway point between 2 and 3. When you don't have live reloading, you likely need to recompile or restart the interpreter to see any change. Rather than rebuilding the image, I put the recompile step in the entrypoint of a development image. I'll mount the code into the container, and run a full JDK instead of just a JRE (or whatever compiler is needed). I use named volumes for any dependency caches so they don't need to download on every restart. Then the method to see the changes is to restart that one container. The steps are identical to a compiled binary outside of a container, stop the old service, recompile, and restart the service, but now it happens inside of a container that should have the same tools used when building the production image.
For option 4, I tend to use a multi-stage build that has stages for build, develop, and release. The build stage pulls in the code and compiles it, the develop stage is the same base image as build but with an entrypoint that does the compile/run, and the release stage copies the result of the build stage into a minimal runtime. Developers then have a compose file for development that creates the development image and runs that with volume mounts and any debugging ports opened.
First of all, docker-compose is just for development and also testing phase, not for production. Example:
With a minimal and basic docker-compose, all your containers will run in the same machine? For development purposes it is ok, but in production, put all the apps in just one machine is a risk
Official link https://docs.docker.com/compose/production/
We will assume
01 java api
01 mysql database
01 web application that needs the api
all of these applications are already in production
Quick Answer
If you need to fix or add new feature to the java api, I advice you to use an ide like eclipse or IntelliJ Idea. Why?
Because java needs compilation.
Compile inside a docker container will take more time due to maven dependencies
IDE has code auto completion
etc
In this development phase, Docker helps you with one of its most powerful features: "Bring the production containers to your localhost". Yeah, in this case, docker-compose.yml is the best option because with one file, you could start everything you need : mysql database and web app but not your java api. Open your java api with your favorite ide.
Anyway if you want to use docker to "develop", you just need the Dockerfile and perform a docker build ... when you need to run your source code in your localhost
Basic Devops Life cycle with docker
Developer push source code changes using git
Your continuous integration (C.I) platform detect this change and perform
docker build ... (In this step, unit test are triggered)
docker push to your private hub. Container is uploaded in this step and will be used to deployments on other servers.
docker run or container deploy to the next environment : testing
Human testers ,selenium or another automation start their work
If no errors are detected, your C.I perform perform a final deploy of the uploaded container to your production environment. No docker build are required, just deploy or docker run.
Some Tips
Docker features are awesome but sometimes add too much complexity. So stop using volumes , hard disk dependency, logs, or complex configurations. If you use volumes, what will happen when your containers are in different hosts?
Java and Nodejs are a stable languages and your rest api or web apps does not need crazy configurations. Just maven compilation and java -jar ... or npm install and npm run start.
For logs you could use https://www.graylog.org/, google stasckdriver or another log management.
And like Heroku, stop using hard disk dependency as much as possible. In heroku platform disk are disposable, it means disappear when app is restarted. So instead of local file storage, you could use another file storage service with a lot of functionalities.
With this approaches, your containers can be deployed anywhere in a simple way
I'm using something similar to your 3rd scenario for my web dev, but it is Node-based. So I have 3 docker-compose files (actually 4, one is base and having all common stuff for others) for dev, staging and production environments.
Staging docker-compose config is similar to production config excluding SSL, ports and other things that may not allow to use it locally.
I have a separate container for each service (like DB, queue), and for dev, I also have additional dev DB and queue containers mostly for running auto-tests. In dev environment, all source are mounted into containers, so it allows to use IDE/editor of choice outside the container, and see changes inside.
I use supervisor to manage my workers inside a container with workers and have some commands to restart my workers manually when I need this. Maybe you can have something similar to recompile/restart your Java app. Or if you have an idea of how to organize app source code changes detection and your app auto-reloading, than could be the best variant. By the way, you gave me an idea to research something similar suitable for my case.
For staging and production environment, my source code is included inside the corresponding container using production Dockerfile. And I have some commands to restart all stuff using an environment I need, and this typically includes rebuilding containers, but because of Docker cache, it doesn't take much time (about 20 seconds). And taking into account that switching between environments is not a too frequent operation I feel quite comfortable with this.
Production docker-compose config is used only during deployment because it enables SSL, proper ports and has some additional production stuff.
Update for details on backend app restarting using Supervisor:
This is how I use it in my projects:
A part of my Dockerfile with installing Supervisor:
FROM node:10.15.2-stretch-slim
RUN apt-get update && apt-get install -y \
# Supervisor
supervisor \
...
...
# Configs for services/workers managed by supervisor
COPY some/path/worker-configs/*.conf /etc/supervisor/conf.d/
This is an example of one of Supervisor configs for a worker:
[program:myWorkerName]
command=/usr/local/bin/node /app/workers/my-worker.js
user=root
numprocs=1
stopsignal=INT
autostart=true
autorestart=true
startretries=10
In this example in your case command should run your Java app.
And this is an example of command aliases for convenient managing Supervisor from outside of containers. I'm using Makefile as a universal runner of all commands, but this can be something else.
# Used to run all workers
su-start:
#docker exec -t MY-WORKERS-CONTAINER-NAME supervisorctl start all
# Used to stop all workers
su-stop:
#docker exec -t MY-WORKERS-CONTAINER-NAME supervisorctl stop all
# Used to restart all workers
su-restart:
#docker exec -t MY-WORKERS-CONTAINER-NAME supervisorctl restart all
# Used to check status of all workers
su-status:
#docker exec -t MY-WORKERS-CONTAINER-NAME supervisorctl status
As I described above these Supervisor commands need to be run manually, but I think it is possible to implement maybe another Node-based worker or some watcher outside of a container with workers that will detect file system changes for sources directory and run these commands automatically. I think it is possible to implement something like this using Java as well like this or this.
On the other hand, it needs to be done carefully to avoid constant restarting workers on every little change.
currently my web application is running on a server, where all the services (nginx, php, etc.) are installed directly in the host system. Now I wanted to use docker to separate these different services into specific containers. Nginx and php-fpm are working fine. But in the web application pdfs can be generated, which is done using wkhtmltopdf and as I want to follow the single-service-per-container pattern, I want to add an additional container which houses wkhtmltopdf and takes care of this specific service.
The problem is: how can I do that? How can I call the wkhtmltopdf binary from the php-fpm container?
One solution is to share the docker.socket, but that is a big security flaw, so I really don‘t like to it.
So, is there any other way to achieve this? And isn‘t this "microservice separation" one of the main purposes/goals of docker?
Thanks for your help!
You can't directly call binaries from one container to another. ("Filesystem isolation" is also a main goal of Docker.)
In this particular case, you might consider "generate a PDF" as an action your service takes and not a separate service in itself, and so executing the binary as a subprocess is a means to an end. This doesn't even raise any complications since presumably mkhtmltopdf isn't a long-running process, you'll launch it once per request and not respond until the subprocess runs to completion. I'd install or include it in the Dockerfile that packages your PHP application, and be architecturally content with that.
Otherwise the main communication between containers is via network I/O and so you'd have to wrap this process in a simple network protocol, probably a minimal HTTP service in your choice of language/framework. That's probably not worth it for this, but it's how you'd turn this binary into "a separate service" that you'd package and run as a separate container.
I sucessfully managed to complete with my Grail's new website and now i want to run it on my machine to acess it everywhere. I would like to know what is the best approach to do that, i'm a bit noob in what concerns servers and connections. Any help would be aprecciated.
Jm
You need a Java servlet container. The quickest and easiest approach is probably to use Jetty on a Linux system -- most will allow you to install it directly. This allows you run a deployed system from a "war" file. Basically, you would do something like:
grails war
To build the war file, and then copy that (it'll be created in the target directory, with a name based on your application name and version) to the webapps directory for Jetty. On my (Ubuntu) system, that's /var/lib/jetty/webapps/. If you name it root.war, it will serve URLs from the root of the server configuration (typically on port 8080), so http://myhost.mydomain:8080/ will be passed to your Grails application. You'll need to restart Jetty to pick up the new root.war file, e.g., sudo /etc/init.d/jetty restart
Jetty is not the most flexible or powerful servlet container, but it is probably the quickest way to get something up and running, and you can explore more powerful alternatives (Tomcat being an obvious one) as you have time.
Unless you need persistent storage in your app (e.g. end users uploading pictures, etc), you can use Cloud Foundry. It's free for now and makes deployment very easy.
http://blog.springsource.com/2011/04/12/one-step-deployment-with-grails-and-cloud-foundry/
I've been using is via STS and it works really well. There's just one really annoying thing and that's the fact that STS ends up doing a build war with every change.
There's a cloud foundry plugin that gives you command line deployment.
http://www.grails.org/plugin/cloud-foundry
Or there's a Cloud Foundry UI plugin that "provides a simple monitoring UI for your applications deployed to Cloud Foundry. It uses the same API as the Cloud Foundry plugin but is more convenient since runs in a web browser."
http://www.grails.org/plugin/cloud-foundry-ui
I would like to achieve the following. I have a C# server application which is run by a Windows Service. The service currently requires that the server application is located in a specific directory.
Is it possible to create a Windows Service that takes a directory at start and run the application in that directory? How do you do that?
Can such a "configurable" service be used to start multiple application (executables with same name but located in different directories). This would be used to run different versions of a server application in parallel. Or do you need one service per running instance?
Yes, simply set the context to reflect the desired environment.To do this use Environment.SetEnvironmentVariable.
A single service can start many applications, each with its environment. Use a configuration file or persistent data in the registry.