Docker Volumes explained in 6 minutes

Key Takeaways

[Music] so in this video we're gonna learn about docker volumes in a natural docker volumes are used for data persistence in docker so for example if you have databases or other stateful applications you would want to use docker volumes for that so what are the specific use cases when you need docker volumes so container runs on a host let's say we have a database container and a container has a virtual file system where the data is usually stored but here there is no persistence so if I were to remove the container or stop it and restart the container then the data in this virtual file system is gone and it starts from a fresh state which is obviously not very practical because I want to save the changes that my application is making in the database and that's where I need docker volumes so what are the docker volumes exactly so on a host we have a physical file system right and the way volumes work is that we plug the physical file system path it could be a folder a directory and we plug it into the containers file system path so in simple terms a directory a folder on a host file system is mounted into a directory or folder in the virtual file system of docker so what happens is that when it container rights to its file system it gets replicated or automatically written on the host file system directory and vice-versa so if I were to change something on the host file system it automatically appears in the container as well so that's why when a container restarts even if it starts from a fresh state in its own virtual file system it gets the data automatically from that from the host because the data is still there and that's how data is populated on the startup of a container every time you restart now there are different types of docker volumes and so different ways of creating them usually the way to create docker volumes is using the kourin command so in the docker run there is an option called - V and this is where we define the connection of the reference between the host directory and the container directory and this type of volume definition is called a host volume and the main characteristic of this one is that you decide where on the host file system that reference is made so which folder on the host file system you mount into the container so the second type is where you create a volume just by referencing the container directory so you don't specify which directory on the host should be mounted but that's taking care of the docker itself so that directory is first of all automatically created by docker under the VAR lip docker volumes so for each container there will be a folder generated that gets mounted automatically to the container and this type of volumes are called anonymous volumes because you don't have a reference to this automatically generated folder basically just have to know the path and the third volume type is actually an improvement of the anonymous volumes and it specifies the name of that folder on the host file system and the name is up to you it just to reference the directory and that type of volumes are called named volumes so in this case compared to anonymous volumes you have you can actually reference that volume just by name so you don't have to know exactly the path so from these three types the mostly used one and the one that you should be using in production is actually the named volumes because they are additional benefits to letting docker actually manage those volume directories on the host now they showed how to create docker volumes using docker run commands but if you're using docker compose it's actually the same so this actually shows how to use volume definitions in a docker compose and this is pretty much the same as in docker run commands so we have volumes at buuuut and underneath you define your volume definition just like you would in this - B option and here we use a named volume so DB - data will be the name reference name that you can just think of it could be anything and inviolable data is the path in the container then you may have some other containers and at the end so in the same level as the services you would actually list all the volumes that you have defined you define at least volumes that you want to mount into the containers so if you were to create volumes for different containers you would list them all here and on the container level then you actually define under which path that specific volume can be mounted and the benefit of that is that you can actually mount a reference of the same folder on a host to more than one containers and that would be beneficial if those containers need to share the data in this case you would mount the same volume name or reference to two different containers and you can mount them in two different paths inside of the container thanks for watching the video I hope it was helpful and if it was don't forget to like it if you want to be notified whenever a new video comes out then subscribe to my channel if you have any questions if something wasn't clear in the video please post them in the comment section below and I will try to answer them so thank you and see you in the next video