I have an application which, for local development, has multiple Docker containers (organized under Docker Compose). One of those containers is a Postgres 10 instance, based on the official postgres:10 image. That instance has its data directory mounted as a Docker volume, which persists data across container runs. All fine so far.
As part of testing the creation and initialization of the postgres cluster, it is frequently the case that I need to remove the Docker volume that holds the data. (The official postgres image runs cluster init if-and-only-if the data directory is found to be empty at container start.) This is also fine.
However! I now have a situation where in order to test and use a third party Postgres extension, I need to load around 6GB of (entirely static) geocoding lookup data into a database on the cluster, from Postgres backup dump files. It's certainly possible to load the data from a local mount point at container start, and the resulting (very large) tables would persist across container restarts in the volume that holds the entire cluster.
Unfortunately, they won't survive the removal of the docker volume which, again, needs to happen with some frequency. I am looking for a way to speed up or avoid the rebuilding of the single database which holds the geocoding data.
Approaches I have been or currently am considering:
Using a separate Docker volume on the same container to create persistent storage for a separate Postgres tablespace that holds only the geocoder database. This appears to be unworkable because while I can definitely set it up, the official PG docs say that tablespaces and clusters are inextricably linked such that the loss of the rest of the cluster would render the additional tablespace unusable. I would love to be wrong about this, since it seems like the simplest solution.
Creating an entirely separate container running Postgres, which mounts a volume to hold a separate cluster containing only the geocoding data. Presumably I would then need to do something kludgy with foreign data wrappers (or some more arcane postgres admin trickery that I don't know of at this point) to make the data seamlessly accessible from the application code.
So, my question: Does anyone know of a way to persist a single database from a dockerized Postgres cluster, without resorting to a dump and reload strategy?
If you want to speed up then you could convert your database dump to a data directory (import your dump to a clean postgres container, stop it and create a tarball of the data directory, then upload it somewhere). Now when you need to create a new postgres container use use a init script to stop the database, download and unpack your tarball to the data directory and start the database again, this way you skip the whole db restore process.
Note: The data tarball has to match the postgres major version so the container has no problem to start from it.
If you want to speed up things even more then create a custom postgres image with the tarball and init script bundled so everytime it starts then it will wipe the empty cluster and copy your own.
You could even change the entrypoint to use your custom script and load the database data, then call docker-entrypoint.sh so there is no need to delete a possible empty cluster.
This will only work if you are OK with replacing the whole cluster everytime you want to run your tests, else you are stuck with importing the database dump.
Related
I accidentally deleted a volume of docker mongo-data:/data/db , i have a copy of that folder , now the problem is when i run docker-compose up mongodb container doesn't start and gives an error of mongo_1 exited with code 14 below more details of the error and the mongo-data folder , can you someone help me please
in docker-compose.yml
volumes:
- ./mongo-data:/data/db
Restore from backup files
A step-by-step process to repair the corrupted files from a failed mongodb in a docker container:
! Before you start, make copy of the files. !
Make sure you know which version of the image was running in the container
Spawn new container with to run the repair process as follows
docker run -it -v <data folder>:/data/db <image-name>:<image-version> mongod --repair
Once the files are repaired, you can start the containers from the docker-compose
If the repair fails, it usually means that the files are corrupted beyond repair. There is still a chance to repair it with exporting the data as described here.
How to secure proper backup files
The database is constantly working with the files, so the files are constantly changed on the disks. In addition, the database will keep some of the changes in the internal memory buffers before they are flushed to the filesystem. Although the database engines are doing very good job to assure the the database can recover from abrupt failure by using the 2-stage commit process (first update the transaction-log than the datafile), when the files are copied there could be a corruption that will prevent the database from recovery.
Reason for such corruption is that the copy process is not aware of the database written process progress, and this creates a racing condition. With very simple words, while the database is in middle of writing, the copy process will create a copy of the file(s) that is half-updated, hence it will be corrupted.
When the database writer is in middle of writing to the files, we call them hot files. hot files are term from the OS perspective, and MongoDB also uses a term hot backup which is a term from MongoDB perspective. Hot backup means that the backup was taken when the database was running.
To take a proper snapshot (assuring the files are cold) you need to follow the procedure explained here. In short, the command db.fsyncLock() that is issued during this process will inform the database engine to flush all buffers and stop writing to the files. This will make the files cold, however the database remains hot, hence the difference between the terms hot files and hot backup. Once the copy is done, the database is informed to start writing to the filesystem by issuing db.fsyncUnlock()
Note the process is more complex and can change with different version of the databse. Here I give a simplification of it, in order to illustrate the point about the problems with the file snapshot. To secure proper and consistent backup, always follow the documented procedure for the database version that you use.
Suggested backup method
Preferred backup should always be the data dump method, since this assures that you can restore even in case of upgraded/downgraded database engines. MongoDB provides very useful tool called mongodump that can be used to create database backups by dumping the data, instead by copy of the files.
For more details on how to use the backup tools, as well as for the other methods of backup read the MongoDB Backup Methods chapter of the MondoDB documentation.
I have a dockerfile for frontend, one for backend, and one for the database.
In the backend portion of the project, I have a dockerfile and a docker-compose.yml file.
the dockerfile is great for the backend because it configures the backend, copies and sets up the information etc. I like it alot.
The issue i have come to though is that if i can easily create a dockerfile for the dbms, but it requires me to put it in a different directory, where i was hoping to just define it in the same directory as the backend, and because of the fact the backend and the dbms is so tightly coupled, i figured this is where docker-compose would go.
My issue I ran into is that in a compose file, I cant do a COPY into the dbms container. I would just have to create another dockerfile to set that up. I was thinking that would work.
When looking on github, there was a big enhancement thread about it, but the closest people would get is just creating volume relationship, which fails to do what I want.
Ideally, All i want to be able to do is to stand up a postgres dbms in a fashion such that i could conduct load balancing on it later down the line with 1 write, 5 read or something, and have its initial db defined in my one sql file.
Am I missing something? I thought i was going about it correctly, but maybe I need to create a whole new directory with a dockerfile for the dbms.
Thoughts on how I should accomplish this?
Right now i was doing something like:
version: '2.0'
services:
backend:
build: .
ports:
- "8080:8080"
database:
image: "postgres:10"
environment:
POSTGRES_USER: "test"
POSTGRES_PASSWORD: "password"
POSTGRES_DB: "foo"
# I shouldnt have volumes as it would copy the entire folder and its contents to db.
volumes:
- ./:/var/lib/postgresql/data
To copy things with docker there an infinite set of possibilities.
At image build time:
use COPY or ADD instructions
use shell commands including cp,ssh,wget and many others.
From the docker command line:
use docker cp to copy from/to hosts and containers
use docker exec to run arbitrary shell commands including cp, ssh and many others...
In docker-compose / kubernetes (or through command line):
use volume to share data between containers
volume can be local or distant file systems (network disk for example)
potentially combine that with shell commands for example to perform backups
Still how you should do it dependy heavily of the use case.
If the data you copy is linked to the code and versionned (in the git repo...) then treat as it was code and build the image with it thanks to the Dockerfile. This is for me a best practice.
If the data is a configuration dependrnt of the environement (like test vs prod, farm 1 vs farm 2), then go for docker config/secret + ENV variables.
If the data is dynamic and generated at production time (like a DB that is filled with user data as the app is used), use persistant volumes and be sure you understand well the impact of container failure for your data.
For a database in a test system it can make sense to relauch the DB from a backup dump, a read only persistant volume or much simpler backup the whole container at a known state (with docker commit).
Almost the same as Import osm data in Docker postgresql BUT I want to load the osm data into the postgres via osm2pgsql during the docker build phase.
The reason for this are:
I only want to load a fixed osm file inside my postgres, meaning this data will not change.
I want to reuse this docker image as many times as possible.
It is not possible to mount any volume with my current environment.
I know that this will make the docker image big but that is something I already took into consideration.
Many suggestions for integration testing which includes Postgres Database say that I can initdb a new whole cluster in RAM disk and work on it.
As far as I understand initdb is a new folder like thing related to databases.
According to Postgres docs:
initdb creates a new PostgreSQL database cluster. A database cluster is a collection of databases that are managed by a single server instance.
Does it create a new server? Or a new Database?
Creating a database cluster consists of creating the directories in which the database data will live, generating the shared catalogue tables (tables that belong to the whole cluster rather than to any particular database), and creating the template1 and Postgres databases. When you later create a new database, everything in the template1 database is copied. (Therefore, anything installed in template1 is automatically copied into each database created later.) The Postgres database is a default database meant for use by users, utilities and third party applications.
Does the above sentence mean that from now on whatever database is created it is stored in that new "cluster"? If not how to create tables in such a cluster of RAM disk?
How can I use it to set it up for testing?
In the terminology your image uses (from pgAdmin?), initdb would create the data directory for a new “server”.
In PostgreSQL, this is not called a server, but a database cluster. It has a data directory, which is created with initdb. If you start the cluster with pg_ctl start, a PostgreSQL server process (called postmaster) is started, which listens for incoming connections and starts backend processes that work on the data directory.
There can be more than one PostgreSQL database clusters on one machine, you just have to give them different port numbers.
It should be no problem to run initdb to create a database cluster for your integration tests. After initdb you have to edit postgresql.conf appropriately (e.g. to set port) and start the postmaster with pg_clt start -D <data directory>.
I am currently moving some data around and I am running into an interesting issue.
I have a CentOS server (6.3) up and running with Postgres 9.2 on a server with limited built in disk space; however, I do have a large amount of extremely reliable external network disk space available.
I have set the tablespace to a directory on this storage devise for my database and everything seems to be working well, until...
I realized that I have a large amount of BLOB data that needs to be stored in pg_largeobject.
I have been goggling how to set the tablespace of pg_largeobject and I did find some results, but they are horribly out dated.
I did find one article that looks promising, but I'm hesitant because the thread also references that things will/should have changed.
I have two questions...
In an ideal world, I would like to move all of postgres (including pg_largeobject) onto this external storage for ease of maintenance. Is this possible?
If not, how can I get pg_largeobject to use my network storage?
As you alluded to, your best bet is to move the entirety of PostgreSQL onto the remote storage, assuming that storage uses a reliable file network block device like iSCSI, ATAoE or NBD. I wouldn't recommend running Pg on NFS, and running it on CIFS/SMBFS just won't work.
Just:
Make a backup
Take a note of the output of SHOW data_directory; in psql
Shut PostgreSQL down
Move the data directory (the folder containing pg_xlog, pg_clog, etc) to the remote storage
Adjust the permissions on the parent directories for the datadir's new location to make sure the postgres user, postgres, group or others permissions block has at least execute on each parent directory so it can traverse the tree.
Adjust your system startup scripts to set the new location as the PostgreSQL datadir or symlink the old datadir location (output by SHOW data_directory) to the new location.
Start PostgreSQL
Unfortunately, different systems and packages find the datadir different ways. Debian/Ubuntu use pg_wrapper, for example.