When does Docker Redis store on a volume?
That store it on a volume every command?
I want to know when Redis will be backed up.
Redis persists data to disk based on configuration. There are config options to persist every command or periodically and in different formats (RDB or AOF).
To understand how Redis data gets backed up, please go thru this link
https://redis.io/docs/management/persistence/.
In your case, since Redis is running inside Docker container make sure to mount a volume that is outside container. Otherwise data will be lost after container restart.
Related
I'm using named volumes to persist data on Host machine in the cloud.
I want to take backup of these volumes present in the docker environment so that I can reuse them on critical incidents.
Almost decided to write a python script to compress the specified directory on the host machine and push it to the AWS S3.
But I would like to know if there is any other approaches to this problem?
docker-volume-backup may be helpful. It allows you to back up your Docker volumes to an external location or to a S3 storage.
Why use a Docker container to back up a Docker volume instead of writing your own Python script? Ideally you don't want to make backups while the volume is being used, so having a container on your docker-compose able to properly stop your container before taking backups can effectively copy data without affecting the application performance or backup integrity.
There's also this alternative: volume-backup
Trying to make sure I understand the proper usage of docker volumes. If I have a container running MongoDB that I plan to start and stop do I need a volume configured with I "docker run" the first time? My understanding is that if use Docker run once, then docker stop/start my data is saved inside the container. The volume is more useful if multiple containers want access to the data. Is that accurate or am I misunderstanding something?
Starting and stopping a container will not delete the container specific data. However, you upgrade containers by replacing them with new containers. Any changes to the container specific read/write layer will be lost when that happens, and the new container will go back to it's initial state. If there are files inside your container that you want to preserve when the container is replaced, then you need to store those files in a volume, and then mount that same volume in the new container.
I have a following question:
If changes on storage are persist between restartings of container ?
For example, we add some rows to mysql database and restart container. If added rows are present in database after restart ?
Yes they are. For each container you run, a docker volume (docker volume -ls to list them) is created.
However if you remove the container or create a new one for some reason, all the changes will be lost.
For a database, it is recommended to use shared volumes between host and the container, to be able to backup the data.
You can see which volume is used by your container using docker inspect.
HiTo persist the data between restartings of container, you need to mount a directory from host to the container so that it's visible to the container.
please check this how to share a directory for mysql which will help to you
I am new to both docker and redis. I have configured serverA to run redis inside docker. The redis database has been pre-seeded with a thousand key/value pairs. I can confirm the data has been persisted in this container. I then created a new docker image from this container, uploaded it to my docker repository.
On serverB, I pulled the redis image "redis-preseeded" and got it started. Using the redis-cli tool when I connect and issue the 'info keyspace' command, the keyspace is empty, suggesting none of the data made it across. What am I doing wrong?
Are you is using the official image for Redis?
https://hub.docker.com/_/redis/
Dockefile for the redis:3.2.0-alpine release
It has a volume declared:
..
VOLUME /data
WORKDIR /data
..
Volumes are described in the documentation. In a nutshell what the authors are doing is configuring Redis to store data on an external disk volume that will be maintained by the docker engine. Not only is this more efficient it also allows users to keep the data separate to the container using it.
Labouring the point a snapshot of the image will contain no data (if you think about it this is a good thing).
Once you understand these concepts then it becomes more obvious how data can be moved between servers:
Backup, Restore and Migrate data volumes
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