Use... In a production environment Docker , It is often necessary to persist the data , Or you need to share data between multiple containers , This inevitably involves data management operations for containers .
Mode one 、Docker cp command
docker cp : Used for data copy between container and host . grammar
# Documents in the container copy to The host machine docker cp [OPTIONS] CONTAINER:SRC_PATH DEST_PATH|-
# Host file copy to In container docker cp [OPTIONS] SRC_PATH|- CONTAINER:DEST_PATH
OPTIONS explain ： -L : Keep links in source target
The operation sample ：
Host to container
Container to host
notes ： Although he can manage this way, the data does not blend , I can't use , Just to understand
Mode two 、Docker Data volume
1. What is? volume
Want to know Docker Volume, First we need to know Docker How does the file system work .Docker Images are made up of multiple file systems ( Read-only layer ) It's superimposed . When we start a container ,Docker The mirror layer is loaded and a read-write layer is added to it . If the running container modifies an existing file , Then the file will be copied from the read-only layer under the read-write layer to the read-write layer , A read-only version of the file still exists , It is hidden by a copy of the file in the read-write layer . When the delete Docker Containers , And restart through this image , Previous changes will be lost . stay Docker in , The combination of the read-only layer and the read-write layer at the top is called Union FIle System( Federated file system ).
In order to be able to preserve ( Persistence ) Data and data between shared containers ,Docker Put forward Volume The concept of . Simply speaking ,Volume It's a directory or a file , It can bypass the default federated file system , And in the form of a normal file or directory on the host .
2. Data volume features
• Data volume You can share and reuse between containers
• Changes to the data volume take effect immediately
• Updates to data volumes , It doesn't affect the mirror image
• Data volume The default is always there , Even if the container is deleted
3. Data volume related operations
Usage: docker volume COMMAND Manage volumes Commands: • create Create a volume • inspect Display detailed information on one or more volumes • ls List volumes • prune Remove all unused local volumes • rm Remove one or more volumes
View all data volumes
Usage: docker volume ls [OPTIONS]
-f, --filter filter Provide filter values (e.g. 'dangling=true')
--format string Pretty-print volumes using a Go template
-q, --quiet Only display volume names
View single or multiple data volume details
Usage: docker volume inspect [OPTIONS] VOLUME [VOLUME...] Display detailed information on one or more volumes Options: -f, --format string Format the output using the given Go template
4. Data volumes use
The use of data volumes , Be similar to Linux Proceed to the directory or file below mount.
The user can go through docker run Of --volume/-v or --mount Option to create a container with data volumes
4.1 --volume Use details
Parameters --volume（ Or abbreviated as -v） Can only be created bind mount. Example ：
docker run --name $CONTAINER_NAME -it \ -v $PWD/$CONTAINER_NAME/app:/app:rw \ -v $PWD/$CONTAINER_NAME/data:/data:ro \ avocado-cloud:latest /bin/bash
• Command format ：[[HOST-DIR:]CONTAINER-DIR[:OPTIONS]]]
• If specified HOST-DIR It has to be an absolute path , If the path does not exist, it will be created automatically
• In the instance rw For reading and writing ,ro As read-only
If it doesn't pass -v Appoint , that Docker It will help us create anonymous data volumes for mapping and mounting by default .
4.2 --mount Use details
about --moun Options , at present Docker Three different types of data volumes are provided for mounting from the host to the container ：
（1）volume： Normal data volume ( The default is this type ),Docker Manage part of the host file system , The default location is /var/lib/docker/volumes Directory ;
（2）bind mount： Bind data volume , Can be stored anywhere in the host system ;
* Be careful ：Dockerfile This usage is not supported in , This is because Dockerfile It's for transplantation and sharing . However , Different operating systems have different path formats , So we can't support .
（3）tmpfs： Temporary data volume , The mount is stored in the memory of the host system , It doesn't write to the host's file system ;
The schematic diagram of the three methods is shown below ：
4.3 -v And -mount The difference between
-mount It can support the creation of data volumes for cluster services , and -v no way .
4.4 Additional explanation
（1）Docker The default permissions for mounting data volumes are read and write , Users can also use :ro Specified as read-only .
（2）（--mount It basically includes --volume Optional attribute content of ） Official recommended use --mount The way , The text is as follows ：
Even though there is no plan to deprecate
--volume, usage of
--mount is recommended.
Mode three 、Docker Data volume container
The data volume container is also a container , But its purpose is to provide data volumes for other containers to mount , If users need to share some continuously updated data among multiple containers , The easiest way is to use a data volume container .
Data volume data backup
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