this is my second day working with Docker, can you help me with a solution for this typical case:
Currently, our application is a combination of Java Netty server, Tomcat, python flask, MariaDB.
Now we want to use Docker to make the deployment more easily.
My first idea is to create 1 Docker Image for environment (CentOS + Java 8 + Python 3), another image for MariaDB, and 1 Image for application.
So the docker-compose.yml should be like this
version: '2'
services:
centos7:
build:
context: ./
dockerfile: centos7_env
image:centos7_env
container_name: centos7_env
tty: true
mariadb:
image: mariadb/server:10.3
container_name: mariadb10.3
ports:
- "3306:3306"
tty: true
app:
build:
context: ./
dockerfile: app_docker
image: app:1.0
container_name: app1.0
depends_on:
- centos7
- mariadb
ports:
- "8081:8080"
volumes:
- /home/app:/home/app
tty: true
The app_dockerfile will be like this:
FROM centos7_env
WORKDIR /home/app
COPY docker_entrypoint.sh ./docker_entrypoint.sh
ENTRYPOINT ["docker_entrypoint.sh"]
In the docker_entrypoint.sh there should couple of commands like:
#!/bin/bash
sh /home/app/server/Server.sh start
sh /home/app/web/Web.sh start
python /home/app/analyze/server.py
I have some questions:
1- Is this design good, any better idea for this?
2- Should we separate image for database like this? Or we could install database on OS image, then do commit?
3- If run docker-compose up, will docker create 2 containers for OS image and app image which based on OS image?, is there anyway to just create container for app (which run on Centos already)?
4- If the app dockerfile not base on OS image, but use FROM SCRATCH, so can it run as expected?
Sorry for long question, Thank you all in advance!!!
One thing to understand is that Docker container is not a VM - they are much more lightweight, so you can run many containers on a single machine.
What I usually do is run each service in its own container. This allows me to package only stuff related to that particular service and update each container individually when needed.
With your example I would run the following containers:
MariaDB
Container running /home/app/server/Server.sh start
Container running /home/app/web/Web.sh start
Python container running python /home/app/analyze/server.py
You don't really need to run centos7 container - this is just a base image which you used to build another container on top of it. Though you would have to build it manually first, so that you can build other image from it - I guess this is what you are trying to achieve here, but it makes docker-compose.yml a bit confusing.
There's really no need to create a huge base container which contains everything. A better practice in my opinion is to use more specialized containers. For example in you case for Python you could have a container which container Python only, for Java - your preferred JDK.
My personal preference is Alpine-based images and you can find many official images based on it: python:<version>-alpine, node:<verion>-alpine, openjdk:<version>-alpine (though I'm not quite sure about all versions), postgres:<version>-alpine and etc.
Hope this helps. Let me know if you have other questions and I will try to address them here.
Related
I have a general question about DockerHub and GitHub. I am trying to build a pipeline on Jenkins using AWS instances and my end goal is to deploy the docker-compose.yml that my repo on GitHub has:
version: "3"
services:
db:
image: postgres
environment:
POSTGRES_USER: user
POSTGRES_PASSWORD: password
volumes:
- ./tmp/db:/var/lib/postgresql/data
web:
build: .
command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
volumes:
- .:/myapp
ports:
- "3000:3000"
depends_on:
- db
environment:
POSTGRES_USER: user
POSTGRES_PASSWORD: password
POSTGRES_HOST: db
I've read that in CI/CD pipelines people build their images and push them to DockerHub but what is the point of it?
You would be just pushing an individual image. Even if you pull the image later in a different instance, in order to run the app with the different services you will need to run the container using docker-compose and you wouldn't have it unless you pull it from the github repo again or create it on the pipeline right?
Wouldn't be better and straightforward to just fetch the repo from Github and do docker-compose commands? Is there a "cleaner" or "proper" way of doing it? Thanks in advance!
The only thing you should need to copy to the remote system is the docker-compose.yml file. And even that is technically optional, since Compose just wraps basic Docker commands; you could manually docker network create and then docker run the two containers without copying anything at all.
For this setup it's important to delete the volumes: that require a copy of the application code to overwrite the image's content. You also shouldn't need an override command:. For the deployment you'd need to replace build: with image:.
version: "3.8"
services:
db: *from-the-question
web:
image: registry.example.com/me/web:${WEB_TAG:-latest}
ports:
- "3000:3000"
depends_on:
- db
environment: *web-environment-from-the-question
# no build:, command:, volumes:
In a Compose setup you could put the build: configuration in a parallel docker-compose.override.yml file that wouldn't get copied to the deployment system.
So what? There are a couple of good reasons to structure things this way.
A forward-looking answer involves clustered container managers like Kubernetes, Nomad, or Amazon's proprietary ECS. In these a container runs somewhere in a cluster of indistinguishable machines, and the only way you have to copy the application code in is by pulling it from a registry. In these setups you don't copy any files anywhere but instead issue instructions to the cluster manager that some number of copies of the image should run somewhere.
Another good reason is to support rolling back the application. In the Compose fragment above, I refer to an environment variable ${WEB_TAG}. Say you push out one build a day and you give each a date-stamped tag; registry.example.com/me/web:20220220. But, something has gone wrong with today's build! While you figure it out, you can connect to the deployment machine and run
WEB_TAG=20220219 docker-compose up -d
and instantly roll back, again without trying to check out anything or copy the application.
In general, using Docker, you want to make the image as self-contained as it can be, though still acknowledging that there are things like the database credentials that can't be "baked in". So make sure to COPY the code in, don't override the code with volumes:, do set a sensible CMD. You should be able to start with a clean system with only Docker installed and nothing else, and docker run the image with only Docker-related setup. You can imagine writing a shell script to run the docker commands, and the docker-compose.yml file is just a declarative version of that.
Finally remember that you don't have to use Docker. You can use a general-purpose system-management tool like Ansible, Salt Stack, or Chef to install Ruby on to the target machine and manually copy the code across. This is a well-proven deployment approach. I find Docker simpler, but there is the assumption that the code and all of its dependencies are actually in the image and don't need to be separately copied.
I have two docker images in Nexus repo
1. sql-db
2. main-svc
The main-svc need sql-db in order to run completely.
Can I defined such in gitlab-ci.yml?
Build:
image: test.com/main-svc:1.5
services: test.com/sql-db:1.0
script:
- docker pull test.com/main-svc:1.5
You can do this if you use docker-in-docker, but you don't need to. Simply define two service containers, as such:
build:
image: alpine
services:
- postgres:latest
- redis:latest
script:
- echo "hello world"
I didn't edit your example because I'm a bit confused about why you're using the same container for both the image and the docker pull inside it. My guess is you have a container you're trying to run integration tests with, then you're testing a container which needs to connect to a database as two different services. If not, it would be helpful for you to state what problem you're trying to solve and we can help more.
So I need rolling-updates with docker on my single node server. Until now, I was using docker-compose but unfortunately, I can't achieve what I need with it. Reading the web, docker-swarm seems to be the way to go.
I have found how to run an app with multiple replicas on a single node using swarm:
docker service create --replicas 3 --name myapp-staging myapp_app:latest
myapp:latest being built from my docker-compose.yml:
version: "3.6"
services:
postgres:
env_file:
- ".env"
image: "postgres:11.0-alpine"
volumes:
- "/var/run/postgresql:/var/run/postgresql"
app:
build: "."
working_dir: /app
depends_on:
- "postgres"
env_file:
- ".env"
command: iex -S mix phx.server
volumes:
- ".:/app"
volumes:
postgres: {}
static:
driver_opts:
device: "tmpfs"
type: "tmpfs"
Unfortunately, this doesn't work since it doesn't get the config from the docker-compose.yml file: .env file, command entry etc.
Searching deeper, I find that using
docker stack deploy -c docker-compose.yml <name>
will create a service using my docker-compose.yml config.
But then I get the following error message:
failed to update service myapp-staging_postgres: Error response from daemon: rpc error: code = InvalidArgument desc = ContainerSpec: image reference must be provided
So it seems I have to use the registry and push my image there so that it works. I understand this need in case of a multiple node architecture, but in my case I don't want to do that. (Carrying images are heavy, I don't want my image to be public, and after all, image is here, so why should I move it to the internet?)
How can I set up my docker service using local image and config written in docker-compose.yml?
I could probably manage my way using docker service create options, but that wouldn't use my docker-compose.yml file so it would not be DRY nor maintainable, which is important to me.
docker-compose is a great tool for developers, it is sad that we have to dive into DevOps tools to achieve such common features as rolling updates. This whole swarm architecture seems too complicated for my needs at this stage.
You don't have to use registeries in your single node setup. you can build your "app" image on your node from a local docker file using this command -cd to the directory of you docker file-
docker build . -t my-app:latest
This will create a local docker image on your node, this image is only visible to your single node which is benefitial in your use case but i wouldn't recommend this in a production setup.
You can now edit the compose file to be:
version: "3.6"
services:
postgres:
env_file:
- ".env"
image: "postgres:11.0-alpine"
volumes:
- "/var/run/postgresql:/var/run/postgresql"
app:
image: "my-app:latest"
depends_on:
- "postgres"
env_file:
- ".env"
volumes:
- ".:/app"
volumes:
postgres: {}
static:
driver_opts:
device: "tmpfs"
type: "tmpfs"
And now you can run your stack from this node and it will use your local app image and benefit from the usage of the image [updates - rollbacks ...etc]
I do have a side note though on your stack file. You are using the same env file for both services, please mind that swarm will look for the ".env" file relative/next to the ".yml" file, so if this is not intentional please revise the location of your env files.
Also on a side note this solution is only feasable on a single node cluster and if you scale your cluster you will have to use a registery and registeries dont have to be public, you can deploy a private registery on your cluster and only your nodes can access it -or you can make it public- the accessibility of your registery is your choice.
Hope this will help with your issue.
Instead of docker images, you can directly use the docker file there. please check the below example.
version: "3.7"
services:
webapp:
build: ./dir
The error is because of compose unable to find an image on the Docker public registry.
Above method should solve your issue.
Basically you need to use docker images in order to make the rolling update to work in docker swarm. Also I would like to clarify that you can host a private registry and use it instead of public one.
Detailed Explanation:
When you try out rolling update how docker swarm works is that it sees whether there is a change in the image which is used for the service if so then docker swarm schedules service updation based on the updation criteria's set up and will work on it.
Let us say there is no change to the image then what happens? Simply docker will not apply the rolling update. Technically you can specify --force flag to make it force update the service but it will just redeploy the service.
Hence create a local repo and store the images into that and use that image name in docker-compose file to be used for a swarm. You can secure the repo by using SSL, user credentials, firewall restrictions which is up to you. Refer this for more details on deploying docker registry server.
Corrections in your compose file:
Since docker stack uses the image to create service you need to specify image: "<image name>" in app service like done in postgres service. AS you have mentioned build instruction image-name is mandatory as docker-compose doesn't know what tho name the image as.Reference.
Registry server is needed if you are going to deploy the application in multi-server. Since you have mentioned it's a single node deployment just having the image pulled/built on the server is enough. But private registry approach is the recommended.
My recommendation is that don't club all the services into a single docker-compose file. The reason is that when you deploy/destroy using docker-compose file all the services will be taken down. This is a kind of tight coupling. Of course, I understand that all the other services depend on DB. in such cases make sure DB service is brought up first before other services.
Instead of specifying the env file make it as a part of Docker file instruction. either copy the env file and source it in entry point or use ENV variable to define it.
Also just an update:
Stack is just to group the services in swarm.
So your compose file should be:
version: "3.6"
services:
postgres:
env_file:
- ".env"
image: "postgres:11.0-alpine"
volumes:
- "/var/run/postgresql:/var/run/postgresql"
app:
build: "."
image: "image-name:tag" #the image built will be tagged as image-name:tag
working_dir: /app # note here I've removed .env file
depends_on:
- "postgres"
command: iex -S mix phx.server
volumes:
- ".:/app"
volumes:
postgres: {}
static:
driver_opts:
device: "tmpfs"
type: "tmpfs"
Dockerfile:
from baseimage:tag
COPY .env /somelocation
# your further instructions go here
RUN ... & \
... & \
... && chmod a+x /somelocation/.env
ENTRYPOINT source /somelocation/.env && ./file-to-run
Alternative Dockerfile:
from baseimage:tag
ENV a $a
ENV b $b
ENV c $c # here a,b,c has to be exported in the shell befire building the image.
ENTRYPOINT ./file-to-run
And you may need to run
docker-compose build
docker-compose push (optional needed to push the image into registry in case registry is used)]
docker stack deploy -c docker-compose.yml <stackname>
NOTE:
Even though you can create the services as mentioned here by #M.Hassan I've explained the ideal recommended way.
I have a golang script which interacts with postgres. Created a service in docker-compose.yml for both golang and postgre. When I run it locally with "docker-compose up" it works perfect, but now I want to create one single image to push it to my dockerhub so it can be pulled and ran with just "docker run ". What is the correct way of doing it?
Image created by "docker-compose up --build" launches with no error with "docker run " but immediately stops.
docker-compose.yml:
version: '3.6'
services:
go:
container_name: backend
build: ./
volumes:
- # some paths
command: go run ./src/main.go
working_dir: $GOPATH/src/workflow/project
environment: #some env variables
ports:
- "80:80"
db:
image: postgres
environment: #some env variables
volumes:
- # some paths
ports:
- "5432:5432"
Dockerfile:
FROM golang:latest
WORKDIR $GOPATH/src/workflow/project
CMD ["/bin/bash"]
I am a newbie with docker so any comments on how to do things idiomatically are appreciated
docker-compose does not combine docker images into one, it runs (with up) or builds then runs (with up --build) docker containers based on the images defined in the yml file.
More info are in the official docs
Compose is a tool for defining and running multi-container Docker applications.
so, in your example, docker-compose will run two containers:
1 - based on the go configurations
2 - based on the db configurations
to see what containers are actually running, use the command:
docker ps -a
for more info see docker docs
It is always recommended to run each searvice on a separate container, but if you insist to make an image which has both golangand postrges, you can take a postgres base image and install golang on it, or the other way around, take golangbased image and install postgres on it.
The installation steps can be done inside the Dockerfile, please refer to:
- postgres official Dockerfile
- golang official Dockerfile
combine them to get both.
Edit: (digital ocean deployment)
Well, if you copy every thing (docker images and the yml file) to your droplet, it should bring the application up and running similar to what happens when you do the same on your local machine.
An example can be found here: How To Deploy a Go Web Application with Docker and Nginx on Ubuntu 18.04
In production, usually for large scale/traffic applications, more advanced solutions are used such as:
- docker swarm
- kubernetes
For more info on Kubernetes on digital ocean, please refer to the official docs
hope this helps you find your way.
Can I use one container for software (e.g. apache, php) and other container just for application code - /var/www/ folder ?
If so, how? Any caveats here?
I need it to speed up deployment - building full image takes more time as well as uploading, downloading full image on all instances
Yes you can!
Example(s):
docker-compose.yml:
web:
build: nginx
volumes_from:
- app
...
app:
build: app
...
You would want your "nginx" Dockerfile to look like:
FROM nginx
VOLUME /var/www/html
...
Where `/var/www/html`` is part of your "app" container.
You would hack on "app" either locally and/or via Docker (docker build app, docker run ... app, etc).
When you're reasonably satisfied you can then test the whole integration by doing something like docker-compose up.