I was reading Project Atomic's guidance for images which states that the 2 main use cases for using a volume are:-
sharing data between containers
when writing large files to disk
I have neither of these use cases in my example using an Nginx image. I intended to mount a host directory as a volume in the path of the Nginx docroot in the container. This is so that I can push changes to a website's contents into the host rather then addressing the container. I feel it is easier to use this approach since I can - for example - just add my ssh key once to the host.
My question is, is this an appropriate use of a data volume and if not can anyone suggest an alternative approach to updating data inside a container?
One of the primary reasons for using Docker is to isolate your app from the server. This means you can run your container anywhere and get the same result. This is my main use case for it.
If you look at it from that point of view, having your container depend on files on the host machine for a deployed environment is counterproductive- running the same container on a different machine may result in different output.
If you do NOT care about that, and are just using docker to simplify the installation of nginx, then yes you can just use a volume from the host system.
Think about this though...
#Dockerfile
FROM nginx
ADD . /myfiles
#docker-compose.yml
web:
build: .
You could then use docker-machine to connect to your remote server and deploy a new version of your software with easy commands
docker-compose build
docker-compose up -d
even better, you could do
docker build -t me/myapp .
docker push me/myapp
and then deploy with
docker pull
docker run
There's a number of ways to achieve updating data in containers. Host volumes are a valid approach and probably the simplest way to achieve making your data available.
You can also copy files into and out of a container from the host. You may need to commit afterwards if you are stopping and removing the running web host container at all.
docker cp /src/www webserver:/www
You can copy files into a docker image build from your Dockerfile, which is the same process as above (copy and commit). Then restart the webserver container from the new image.
COPY /src/www /www
But I think the host volume is a good choice.
docker run -v /src/www:/www webserver command
Docker data containers are also an option for mounted volumes but they don't solve your immediate problem of copying data into your data container.
If you ever find yourself thinking "I need to ssh into this container", you are probably doing it wrong.
Not sure if I fully understand your request. But why you need do that to push files into Nginx container.
Manage volume in separate docker container, that's my suggestion and recommend by Docker.io
Data volumes
A data volume is a specially-designated directory within one or more containers that bypasses the Union File System. Data volumes provide several useful features for persistent or shared data:
Volumes are initialized when a container is created. If the container’s base image contains data at the specified mount point, that existing data is copied into the new volume upon volume initialization.
Data volumes can be shared and reused among containers.
Changes to a data volume are made directly.
Changes to a data volume will not be included when you update an image.
Data volumes persist even if the container itself is deleted.
refer: Manage data in containers
As said, one of the main reasons to use docker is to achieve always the same result. A best practice is to use a data only container.
With docker inspect <container_name> you can know the path of the volume on the host and update data manually, but this is not recommended;
or you can retrieve data from an external source, like a git repository
Related
I'm kind of stuck,
I have a docker container that is running, and that container runs some elasticsearch inside.
But I forgot to use volume on the first deploy. So my container has lots of data inside, in a single folder in /app/data.
I would like to use the same container but use volume on that folder, without losing data inside...
So it will be possible to rebuild other containers to use the same volume.
Have you some tips to share?
The important thing is not to remove your container, or you'll lose all that data. I think docker cp is your friend here (docs here). Copy the data to the host, then start another container with a volume.
Once you've secured your data, you can stop and remove the first container.
IOs are very slow in Docker for Mac due to the overhead of syncing files between the host and container. I want to be able to use docker compose to copy my application files to a certain directory in the container, but WITHOUT any kind of syncing/mounting. If I modify my application, I would just do docker-compose restart to create a new container using the updated files. It seems that all docker volume functionality necessitates some kind of syncing to/from the host, which I don't want. How do I accomplish this?
My current volume config, which DOES do syncing, looks like this:
volumes:
- ./application:/var/www/application:cached
Let's say you are trying to dockerise a database (couchdb for example).
Then there are at least two assets you consider volumes for:
database files
log files
Let's further say you want to keep the db-files private but want to expose the log-files for later processing.
As far as I undestand the documentation, you have two options:
First option
define managed volumes for both, log- and db-files within the db-image
import these in a second container (you will get both) and work with the logs
Second option
create data container with a managed volume for the logs
create the db-image with a managed volume for the db-files only
import logs-volume from data container when running db-image
Two questions:
Are both options realy valid/ possible?
What is the better way to do it?
br volker
The answer to question 1 is that, yes both are valid and possible.
My answer to question 2 is that I would consider a different approach entirely and which one to choose depends on whether or not this is a mission critical system and that data loss must be avoided.
Mission critical
If you absolutely cannot lose your data, then I would recommend that you bind mount a reliable disk into your database container. Bind mounting is essentially mounting a part of the Docker Host filesystem into the container.
So taking the database files as an example, you could image these steps:
Create a reliable disk e.g. NFS that is backed-up on a regular basis
Attach this disk to your Docker host
Bind mount this disk into my database container which then writes database files to this disk.
So following the above example, lets say I have created a reliable disk that is shared over NFS and mounted on my Docker Host at /reliable/disk. To use that with my database I would run the following Docker command:
docker run -d -v /reliable/disk:/data/db my-database-image
This way I know that the database files are written to reliable storage. Even if I lose my Docker Host, I will still have the database files and can easily recover by running my database container on another host that can access the NFS share.
You can do exactly the same thing for the database logs:
docker run -d -v /reliable/disk/data/db:/data/db -v /reliable/disk/logs/db:/logs/db my-database-image
Additionally you can easily bind mount these volumes into other containers for separate tasks. You may want to consider bind mounting them as read-only into other containers to protect your data:
docker run -d -v /reliable/disk/logs/db:/logs/db:ro my-log-processor
This would be my recommended approach if this is a mission critical system.
Not mission critical
If the system is not mission critical and you can tolerate a higher potential for data loss, then I would look at Docker Volume API which is used precisely for what you want to do: managing and creating volumes for data that should live beyond the lifecycle of a container.
The nice thing about the docker volume command is that it lets you created named volumes and if you name them well it can be quite obvious to people what they are used for:
docker volume create db-data
docker volume create db-logs
You can then mount these volumes into your container from the command line:
docker run -d -v db-data:/db/data -v db-logs:/logs/db my-database-image
These volumes will survive beyond the lifecycle of your container and are stored on the filesystem if your Docker host. You can use:
docker volume inspect db-data
To find out where the data is being stored and back-up that location if you want to.
You may also want to look at something like Docker Compose which will allow you to declare all of this in one file and then create your entire environment through a single command.
I have a Python app using a SQLite database (it's a data collector that runs daily by cron). I want to deploy it, probably on AWS or Google Container Engine, using Docker. I see three main steps:
1. Containerize and test the app locally.
2. Deploy and run the app on AWS or GCE.
3. Backup the DB periodically and download back to a local archive.
Recent posts (on Docker, StackOverflow and elsewhere) say that since 1.9, Volumes are now the recommended way to handle persisted data, rather than the "data container" pattern. For future compatibility, I always like to use the preferred, idiomatic method, however Volumes seem to be much more of a challenge than data containers. Am I missing something??
Following the "data container" pattern, I can easily:
Build a base image with all the static program and config files.
From that image create a data container image and copy my DB and backup directory into it (simple COPY in the Dockerfile).
Push both images to Docker Hub.
Pull them down to AWS.
Run the data and base images, using "--volume-from" to refer to the data.
Using "docker volume create":
I'm unclear how to copy my DB into the volume.
I'm very unclear how to get that volume (containing the DB) up to AWS or GCE... you can't PUSH/PULL a volume.
Am I missing something regarding Volumes?
Is there a good overview of using Volumes to do what I want to do?
Is there a recommended, idiomatic way to backup and download data (either using the data container pattern or volumes) as per my step 3?
When you first use an empty named volume, it will receive a copy of the image's volume data where it's first used (unlike a host based volume that completely overlays the mount point with the host directory). So you can initialize the volume contents in your main image as a volume, upload that image to your registry and pull that image down to your target host, create a named volume on that host, point your image to that named volume (using docker-compose makes the last two steps easy, it's really 2 commands at most docker volume create <vol-name> and docker run -v <vol-name>:/mnt <image>), and it will be populated with your initial data.
Retrieving the data from a container based volume or a named volume is an identical process, you need to mount the volume in a container and run an export/backup to your outside location. The only difference is in the command line, instead of --volumes-from <container-id> you have -v <vol-name>:/mnt. You can use this same process to import data into the volume as well, removing the need to initialize the app image with data in it's volume.
The biggest advantage of the new process is that it clearly separates data from containers. You can purge all the containers on the system without fear of losing data, and any volumes listed on the system are clear in their name, rather than a randomly assigned name. Lastly, named volumes can be mounted anywhere on the target, and you can pick and choose which of the volumes you'd like to mount if you have multiple data sources (e.g. config files vs databases).
I have a Docker container and I am trying to make it so that all of the files in /var/www/ on the container will be saved on the host system at a location (/home/me), and vise-versa. Is it possible to have this shared space between the two?
Would you accomplish this with mount points, or is there a better method?
Thanks
You can use volumes for sharing between container and host.
docker run -v /home/me:/var/www <image>
If you have a fixed files/data, you can add to the image using dockerfile or committing after copying into container. If you want to share rw dir between host and container, you need to use the volumes. Your data will also be persisted even if you remove and recreate a new container.
There are three ways that you can do this
Use volumes. Official docs
Burn the files in your image. Basically include the creation of the files inside the Dockerfile. This means every container container from that image will have an initial state of sorts.
Use data-only containers. These are containers without a running process that contain the data that you need. This also uses volumes. But instead of mounting to the host, your containers mount on the data-only container (which in turn mounts on the host if you want to). This answer will be useful