Just putting out into a blog post some of the things I understand about Docker volumes and bind-mounts. Been doing a bit of reading on these and taking notes.\u00a0<\/p>\n
We have two types of locations that can be mounted into a Docker container. One is where we give the absolute path to a folder or file, the other is where we let Docker manage the location. The first is called a bind mount<\/a>, the second is volumes<\/a>. With volumes we just create a volume by name and Docker puts it in a location managed by it. For instance:<\/p>\n As you can see Docker created a folder under There’s two ways to mount a bind-mount or volume into a container – using a The two switches behave similarly except for one difference when it comes to bind-mounts<\/span>. If the source file or directory does not exist, the Between volumes and bind-mounts there’s one more difference to keep in mind (irrespective of the On the other hand if I were to do the same for a bind-mount, the existing contents of that path are hidden and only any changes are visible.\u00a0<\/p>\n The three files in there are what Docker added for name resolution. And only these three files get copied into the path we mapped.<\/p>\n Something else I found interesting:<\/p>\n This seems useful. I am still playing with Docker so I haven’t figured out how it would be useful, but it seems to be. :)<\/p>\n","protected":false},"excerpt":{"rendered":" Just putting out into a blog post some of the things I understand about Docker volumes and bind-mounts. Been doing a bit of reading on these and taking notes.\u00a0 We have two types of locations that can be mounted into a Docker container. One is where we give the absolute path to a folder or … Continue reading Docker volumes & bind-mounts and existing data<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[912],"tags":[498],"jetpack_publicize_connections":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/posts\/4734"}],"collection":[{"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/comments?post=4734"}],"version-history":[{"count":0,"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/posts\/4734\/revisions"}],"wp:attachment":[{"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/media?parent=4734"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/categories?post=4734"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/rakhesh.com\/wp-json\/wp\/v2\/tags?post=4734"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}$ docker volume create my-test-volume\nmy-test-volume\n\n$ docker inspect my-test-volume\n[\n {\n \"CreatedAt\": \"2020-07-17T18:03:57+01:00\",\n \"Driver\": \"local\",\n \"Labels\": {},\n \"Mountpoint\": \"\/var\/lib\/docker\/volumes\/my-test-volume\/_data\",\n \"Name\": \"my-test-volume\",\n \"Options\": {},\n \"Scope\": \"local\"\n }\n]<\/pre>\n\/var\/lib\/docker\/volumes<\/code> and that’s what will get mounted into the container. (Note<\/strong>: this is in the case of Linux. For macOS Docker runs inside a Linux VM on macOS, so the volume path shown won’t be a path on the macOS file system but will be something in the Linux VM and we can’t access that directly. Not sure how it’s on Windows as I haven’t tried Docker on Windows yet).<\/p>\n-v<\/code> (or --volume<\/code>) switch or using a --mount<\/code> switch. The former is the old way, the latter is the new and preferred way. With the --mount<\/code> switch one can be more explicit.\u00a0<\/p>\n-v<\/code> switch silently creates a new directory while the --mount<\/code> switch throws an error. This is because traditionally the -v<\/code> switch created a directory and that behaviour can’t be changed now. In the case of volumes<\/span> either switch simply creates the volume if it does not exist.\u00a0<\/p>\n-v<\/code> or --mount<\/code> switches). If one were to mount an empty volume to a path which has data in a container, the data in that path is copied into this empty volume (and any further changes are of course stored in this volume).\u00a0<\/p>\n# create a new (empty) volume\n$ docker volume create my_empty_volume\nmy_empty_volume\n\n# mount this to a path with data in the container; as you can see the existing data is visible\n$ docker run -it --rm --mount type=volume,source=my_empty_volume,target=\/etc alpine ls \/etc\nalpine-release inittab opt services\napk issue os-release shadow\nconf.d logrotate.d passwd shells\n\n# now if I mount this previously empty container elsewhere and inspect its data I will see that the contents above were copied into it\n$ docker run -it --rm --mount type=volume,source=my_empty_volume,target=\/tmp2 alpine ls \/tmp2\nalpine-release inittab opt services\napk issue os-release shadow\nconf.d logrotate.d passwd shells<\/pre>\n
$ mkdir docker-data\/empty\n$ docker run --rm -it --mount type=bind,source=$(pwd)\/docker-data\/empty,target=\/etc alpine ls \/etc\nhostname hosts resolv.conf\n\n$ ls docker-data\/empty\/\nhostname hosts resolv.conf<\/pre>\n
# create a new container and mount a volume in it\n$ docker run -dit --mount type=volume,source=my-data-volume,target=\/my-configs alpine\n\n# even though the container has exited I can see it still has a reference to this volume\n$ docker inspect 887f359a6a772a03c0edd0fc | jq '.[] | .Mounts'\n[\n {\n \"Type\": \"volume\",\n \"Name\": \"my-data-volume\",\n \"Source\": \"\/var\/lib\/docker\/volumes\/my-data-volume\/_data\",\n \"Destination\": \"\/my-configs\",\n \"Driver\": \"local\",\n \"Mode\": \"z\",\n \"RW\": true,\n \"Propagation\": \"\"\n }\n]\n\n# now I can create a new container and refer to the volumes in the previous container. it will automatically mount and map them all. \ndocker run -dit --volumes-from 887f359a6a77 alpine\n64131192e38f9b5abdc00fa9c5923bfa626d286b365fd21eaf8e5243f90ebb8c\nrakhesh@pi1:~ $ docker inspect 64131192e38f9b5abdc | jq '.[] | .Mounts'\n[\n {\n \"Type\": \"volume\",\n \"Name\": \"my-data-volume\",\n \"Source\": \"\/var\/lib\/docker\/volumes\/my-data-volume\/_data\",\n \"Destination\": \"\/my-configs\",\n \"Driver\": \"local\",\n \"Mode\": \"\",\n \"RW\": true,\n \"Propagation\": \"\"\n }\n]<\/pre>\n