I have two hosts that run docker service on each host.
Container from host A wanted to uses volume that created from host B.
Is this possible?
noops, both services should be on the same host but there is one thing you can do.
All reused data volumes are mounted on the same paths as in the source
service. Containers must be on the same host in order to share
volumes, so the containers of the new service will deploy to the same
nodes where the source service containers are deployed.
https://docs.docker.com/docker-cloud/apps/volumes/
Possible solution:
mount volume to a host directory
sync that directory between your nodes
You can use NFS to sync directories on all nodes, i have used it myself works fine
Related
I have seen the terms "bind mount" and "host volume" being used in various articles but none of them mention whether they are the same thing or not. But looking at their function, it looks like they are pretty much the same thing. Can anyone answer whether it is the same thing or not? If not, what is the difference?
Ref:
Docker Docs - Use bind mounts
https://blog.logrocket.com/docker-volumes-vs-bind-mounts/
They are different concepts.
As mentioned in bind mounts:
Bind mounts have been around since the early days of Docker. Bind mounts have limited functionality compared to volumes. When you use a bind mount, a file or directory on the host machine is mounted into a container. The file or directory is referenced by its absolute path on the host machine. By contrast, when you use a volume, a new directory is created within Docker’s storage directory on the host machine, and Docker manages that directory’s contents.
And as mentioned in volumes:
Volumes are the preferred mechanism for persisting data generated by
and used by Docker containers. While bind mounts are dependent on the
directory structure and OS of the host machine, volumes are completely
managed by Docker. Volumes have several advantages over bind mounts:
Volumes are easier to back up or migrate than bind mounts.
You can manage volumes using Docker CLI commands or the Docker API.
Volumes work on both Linux and Windows containers.
Volumes can be more safely shared among multiple containers.
Volume drivers let you store volumes on remote hosts or cloud providers, to encrypt the contents of volumes, or to add other functionality.
New volumes can have their content pre-populated by a container.
Volumes on Docker Desktop have much higher performance than bind mounts from Mac and Windows hosts.
A "bind mount" is when you let your container see and use a normal directory in a normal filesystem on your host. Changes made by programs running in the container will be visible in your host's filesystem.
A "volume" is a single file on your host that acts like a whole filesystem visible to the container. You can't normally see what's inside it from the host.
I was able to figure it out.
There are 3 types of storage in Docker.
1. Bind mounts-also known as host volumes.
2. Anonymous volumes.
3. Named volumes.
So bind mount = host volume. They are the same thing. "Host volume" must be a deprecating term though, as I cannot see it in Docker docs. But it can be seen in various articles published 1-2 years ago.
Examples for where it is referred to as "host volume":
https://docs.drone.io/pipeline/docker/syntax/volumes/host/
https://spin.atomicobject.com/2019/07/11/docker-volumes-explained/
This docs page here Manage data in Docker is quite helpful
Volumes are stored in a part of the host filesystem which is managed by Docker (/var/lib/docker/volumes/ on Linux). Non-Docker processes should not modify this part of the filesystem. Volumes are the best way to persist data in Docker.
Bind mounts may be stored anywhere on the host system. They may even be important system files or directories. Non-Docker processes on the Docker host or a Docker container can modify them at any time.
I'm reading a document from Microsoft that states about Docker volumes
Volumes are stored within directories on the host filesystem. Docker
will mount and manage the volumes in the container. Once mounted,
these volumes are isolated from the host machine.
Multiple containers can simultaneously use the same volumes. Volumes
also don't get removed automatically when a container stops using the
volume.
In our example, we can create a directory on our container host and
mount this volume into the container when we create the tracking
portal container. When our tracking portal logs data, we can access
this information via the container host's filesystem. We'll have
access to this log file even if our container is removed.
I'm confused as I understand that the volumes are isolated from the host machine, but how can that be if we can access to the data via the host.
I'm less familiar with Docker on Windows, but I'm sure it's probably the same as Linux in this regard...
Docker volumes are "isolated on the host machine" by being in a particular location with particular permissions on the host's filesystem (i.e. via namespaces). Users/accounts with elevated permissions would still be granted access to those directories/files.
By contrast a bind mount can be made to (pretty much) any directory on the host's file system.
I have two Docker Host with one container each. For example I have a Container A (Host A) and Container B(Host B), Is there a way that all the volumes or mount inside Container A(Host A) will go straight to Container B(Host B)? I'm using Docker Swarm but I can't figure it out with stack.
If i understand correctly the question, when you have two hosts, you can use a shared drive, live NFS or S3. Then you mount this drive on the two hosts and you can have your volume share in container A and B.
How can I achieve a persistent storage for a WebDAV server running on several/any swarm nodes?
It's part of a docker-compose app running on my own vSphere infrastructure.
I was thinking about mounting an external NFS share from insde the containers (at the OS level, not docker volumes) but then how would that be better than having WebDAV outside the swarm cluster?
I can think of 2 options:
Glusterfs
This option is vSphere independent. You can create replicated bricks and store your volumes on them. Exposing same volume to multiple docker hosts. So in case of node failure the container will get restarted on another node and has it's persistent storage with it. You can also mount the persistent data on multiple containers.
There is one catch: Same diskspace will be consumed on multiple nodes.
Docker-Volume-vSphere
This option requires vsphere hosts. You can create docker volumes on vmfs datastores. they will be shared between docker hosts (virtual machines). So in case of failure the container restarts on another node and has persistent data available. Multiple containers can share a single volume.
I am able to run a docker image and can connect log file in a container into a host machine volume .
I wonder how I can differentiate two containers of same running images at same host?
May be container ids can be used but I donot know how I can pass container id into log4j.xml file as a parameter?