go-ceph - Go bindings for Ceph APIs

Introduction

The go-ceph project is a collection of API bindings that support the use of native Ceph APIs, which are C language functions, in Go. These bindings make use of Go's cgo feature. There are three main Go sub-packages that make up go-ceph:

• rados - exports functionality from Ceph's librados
• rbd - exports functionality from Ceph's librbd
• cephfs - exports functionality from Ceph's libcephfs

We aim to provide comprehensive support for the Ceph APIs over time. This includes both I/O related functions and management functions. If your project makes use of Ceph command line tools and is written in Go, you may be able to switch away from shelling out to the CLI and to these native function calls.

Installation

The code in go-ceph is purely a library module. Typically, one will import go-ceph in another Go based project. When building the code the native RADOS, RBD, & CephFS library and development headers are expected to be installed.

On debian based systems (apt) these may be:

libcephfs-dev librbd-dev librados-dev

On rpm based systems (dnf, yum, etc) these may be:

libcephfs-devel librbd-devel librados-devel

To quickly test if one can build with go-ceph on your system, run:

go get github.com/ceph/go-ceph

Once compiled, code using go-ceph is expected to dynamically link to the Ceph libraries. These libraries must be available on the system where the go based binaries will be run. The use of cgo does not allow for fully static binaries.

go-ceph tries to support different Ceph versions. However some functions might only be available in recent versions, and others may be deprecated. In order to work with non-current versions of Ceph, it is required to pass build-tags to the go command line. A tag with the named Ceph release will enable/disable certain features of the go-ceph packages, and prevent warnings or compile problems. For example, to ensure you select the library features that match the "nautilus" release, use:

go build -tags nautilus ....
go test -tags nautilus ....

Supported Ceph Versions

go-ceph version	Supported Ceph Versions	Deprecated Ceph Versions
v0.5.0	nautilus, octopus	luminous, mimic
v0.4.0	luminous, mimic, nautilus, octopus
v0.3.0	luminous, mimic, nautilus, octopus
v0.2.0	luminous, mimic, nautilus
(pre release)	luminous, mimic (see note)

These tags affect what is supported at compile time. What version of the Ceph cluster the client libraries support, and vice versa, is determined entirely by what version of the Ceph C libraries go-ceph is compiled with.

NOTE: Prior to 2020 the project did not make versioned releases. The ability to compile with a particular Ceph version before go-ceph v0.2.0 is not guaranteed.

Documentation

Detailed documentation is available at https://pkg.go.dev/github.com/ceph/go-ceph.

Connecting to a cluster

Connect to a Ceph cluster using a configuration file located in the default search paths.

conn, _ := rados.NewConn()
conn.ReadDefaultConfigFile()
conn.Connect()

A connection can be shutdown by calling the Shutdown method on the connection object (e.g. conn.Shutdown()). There are also other methods for configuring the connection. Specific configuration options can be set:

conn.SetConfigOption("log_file", "/dev/null")

and command line options can also be used using the ParseCmdLineArgs method.

args := []string{ "--mon-host", "1.1.1.1" }
err := conn.ParseCmdLineArgs(args)

For other configuration options see the full documentation.

Object I/O

Object in RADOS can be written to and read from with through an interface very similar to a standard file I/O interface:

// open a pool handle
ioctx, err := conn.OpenIOContext("mypool")

// write some data
bytesIn := []byte("input data")
err = ioctx.Write("obj", bytesIn, 0)

// read the data back out
bytesOut := make([]byte, len(bytesIn))
_, err := ioctx.Read("obj", bytesOut, 0)

if !bytes.Equal(bytesIn, bytesOut) {
    fmt.Println("Output is not input!")
}

Pool maintenance

The list of pools in a cluster can be retreived using the ListPools method on the connection object. On a new cluster the following code snippet:

pools, _ := conn.ListPools()
fmt.Println(pools)

will produce the output [data metadata rbd], along with any other pools that might exist in your cluster. Pools can also be created and destroyed. The following creates a new, empty pool with default settings.

conn.MakePool("new_pool")

Deleting a pool is also easy. Call DeletePool(name string) on a connection object to delete a pool with the given name. The following will delete the pool named new_pool and remove all of the pool's data.

conn.DeletePool("new_pool")

Development

docker run --rm -it --net=host \
  --device /dev/fuse --cap-add SYS_ADMIN --security-opt apparmor:unconfined \
  -v ${PWD}:/go/src/github.com/ceph/go-ceph:z \
  -v /home/nwatkins/src/ceph/build:/home/nwatkins/src/ceph/build:z \
  -e CEPH_CONF=/home/nwatkins/src/ceph/build/ceph.conf \
  ceph-golang

Run against a vstart.sh cluster without installing Ceph:

export CGO_CPPFLAGS="-I/ceph/src/include"
export CGO_LDFLAGS="-L/ceph/build/lib"
go build

Contributing

Contributions are welcome & greatly appreciated, every little bit helps. Make code changes via Github pull requests:

• Fork the repo and create a topic branch for every feature/fix. Avoid making changes directly on master branch.
• All incoming features should be accompanied with tests.
• Make sure that you run go fmt before submitting a change set. Alternatively the Makefile has a flag for this, so you can call make fmt as well.
• The integration tests can be run in a docker container, for this run:

make test-docker

Interactive "Office Hours"

The maintenance team plans to be available regularly for questions, comments, pings, etc for about an hour twice a week. The current schedule is:

• 2:00pm EDT (currently 18:00 UTC) Mondays
• 9:00am EDT (currently 13:00 UTC) Thursdays

We will use the #ceph-devel IRC channel