Managed Grid

This document explains the “Grid Manager” concept and the grid-manager command. Someone operating a grid may choose to use a Grid Manager. Operators of storage-servers and clients will then be given additional configuration in this case.

Overview and Motivation

In a grid using an Introducer, a client will use any storage-server the Introducer announces (and the Introducer will announce any storage-server that connects to it). This means that anyone with the Introducer fURL can connect storage to the grid.

Sometimes, this is just what you want!

For some use-cases, though, you want to have clients only use certain servers. One case might be a “managed” grid, where some entity runs the grid; clients of this grid don’t want their uploads to go to “unmanaged” storage if some other client decides to provide storage.

One way to limit which storage servers a client connects to is via the “server list” (Static Server Definitions) (aka “Introducerless” mode). Clients are given static lists of storage-servers, and connect only to those. This means manually updating these lists if the storage servers change, however.

Another method is for clients to use [client] peers.preferred= configuration option (Client Configuration), which suffers from a similar disadvantage.

Grid Manager

A “grid-manager” consists of some data defining a keypair (along with some other details) and Tahoe sub-commands to manipulate the data and produce certificates to give to storage-servers. Certificates assert the statement: “Grid Manager X suggests you use storage-server Y to upload shares to” (X and Y are public-keys). Such a certificate consists of:

• the version of the format the certificate conforms to (1)

• the public-key of a storage-server

• an expiry timestamp

• a signature of the above

A client will always use any storage-server for downloads (expired certificate, or no certificate) because clients check the ciphertext and re-assembled plaintext against the keys in the capability; “grid-manager” certificates only control uploads.

Clients make use of this functionality by configuring one or more Grid Manager public keys. This tells the client to only upload to storage-servers that have a currently-valid certificate from any of the Grid Managers their client allows. In case none are configured, the default behavior (of using any storage server) prevails.

Grid Manager Data Storage

The data defining the grid-manager is stored in an arbitrary directory, which you indicate with the --config option (in the future, we may add the ability to store the data directly in a grid, at which time you may be able to pass a directory-capability to this option).

If you don’t want to store the configuration on disk at all, you may use --config - (the last character is a dash) and write a valid JSON configuration to stdin.

All commands require the --config option and they all behave similarly for “data from stdin” versus “data from disk”. A directory (and not a file) is used on disk because in that mode, each certificate issued is also stored alongside the configuration document; in “stdin / stdout” mode, an issued certificate is only ever available on stdout.

The configuration is a JSON document. It is subject to change as Grid Manager evolves. It contains a version number in the grid_manager_config_version key which will increment whenever the document schema changes.

grid-manager create

Create a new grid-manager.

If you specify --config - then a new grid-manager configuration is written to stdout. Otherwise, a new grid-manager is created in the directory specified by the --config option. It is an error if the directory already exists.

grid-manager public-identity

Print out a grid-manager’s public key. This key is derived from the private-key of the grid-manager, so a valid grid-manager config must be given via --config

This public key is what is put in clients’ configuration to actually validate and use grid-manager certificates.

grid-manager add

Takes two args: name pubkey. The name is an arbitrary local identifier for the new storage node (also sometimes called “a petname” or “nickname”). The pubkey is the tahoe-encoded key from a node.pubkey file in the storage-server’s node directory (minus any whitespace). For example, if ~/storage0 contains a storage-node, you might do something like this:

grid-manager --config ./gm0 add storage0 $(cat ~/storage0/node.pubkey)

This adds a new storage-server to a Grid Manager’s configuration. (Since it mutates the configuration, if you used --config - the new configuration will be printed to stdout). The usefulness of the name is solely for reference within this Grid Manager.

grid-manager list

Lists all storage-servers that have previously been added using grid-manager add.

grid-manager sign

Takes two args: name expiry_days. The name is a nickname used previously in a grid-manager add command and expiry_days is the number of days in the future when the certificate should expire.

Note that this mutates the state of the grid-manager if it is on disk, by adding this certificate to our collection of issued certificates. If you used --config -, the certificate isn’t persisted anywhere except to stdout (so if you wish to keep it somewhere, that is up to you).

This command creates a new “version 1” certificate for a storage-server (identified by its public key). The new certificate is printed to stdout. If you stored the config on disk, the new certificate will (also) be in a file named like alice.cert.0.

Enrolling a Storage Server: CLI

tahoe admin add-grid-manager-cert

• –filename: the file to read the cert from

• –name: the name of this certificate

Import a “version 1” storage-certificate produced by a grid-manager A storage server may have zero or more such certificates installed; for now just one is sufficient. You will have to re-start your node after this. Subsequent announcements to the Introducer will include this certificate.

Note

This command will simply edit the tahoe.cfg file and direct you to re-start. In the Future(tm), we should consider (in exarkun’s words):

“A python program you run as a new process” might not be the best abstraction to layer on top of the configuration persistence system, though. It’s a nice abstraction for users (although most users would probably rather have a GUI) but it’s not a great abstraction for automation. So at some point it may be better if there is CLI -> public API -> configuration persistence system. And maybe “public API” is even a network API for the storage server so it’s equally easy to access from an agent implemented in essentially any language and maybe if the API is exposed by the storage node itself then this also gives you live-configuration-updates, avoiding the need for node restarts (not that this is the only way to accomplish this, but I think it’s a good way because it avoids the need for messes like inotify and it supports the notion that the storage node process is in charge of its own configuration persistence system, not just one consumer among many … which has some nice things going for it … though how this interacts exactly with further node management automation might bear closer scrutiny).

Enrolling a Storage Server: Config

You may edit the [storage] section of the tahoe.cfg file to turn on grid-management with grid_management = true. You then must also provide a [grid_management_certificates] section in the config-file which lists name = path/to/certificate pairs.

These certificate files are issued by the grid-manager sign command; these should be transmitted to the storage server operator who includes them in the config for the storage server. Relative paths are based from the node directory. Example:

[storage]
grid_management = true

[grid_management_certificates]
default = example_grid.cert

This will cause us to give this certificate to any Introducers we connect to (and subsequently, the Introducer will give the certificate out to clients).

Enrolling a Client: Config

You may instruct a Tahoe client to use only storage servers from given Grid Managers. If there are no such keys, any servers are used (but see https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3979). If there are one or more keys, the client will only upload to a storage server that has a valid certificate (from any of the keys).

To specify public-keys, add a [grid_managers] section to the config. This consists of name = value pairs where name is an arbitrary name and value is a public-key of a Grid Manager. Example:

[grid_managers]
example_grid = pub-v0-vqimc4s5eflwajttsofisp5st566dbq36xnpp4siz57ufdavpvlq

See also https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3507 which proposes a command to edit the config.

Example Setup of a New Managed Grid

This example creates an actual grid, but it’s all just on one machine with different “node directories” and a separate tahoe process for each node. Usually of course each storage server would be on a separate computer.

Note that we use the daemonize command in the following but that’s only one way to handle “running a command in the background”. You could instead run commands that start with daemonize ... in their own shell/terminal window or via something like systemd

We’ll store our Grid Manager configuration on disk, in ./gm0. To initialize this directory:

grid-manager --config ./gm0 create

(If you already have a grid, you can skip ahead.)

First of all, create an Introducer. Note that we actually have to run it briefly before it creates the “Introducer fURL” we want for the next steps:

tahoe create-introducer --listen=tcp --port=5555 --location=tcp:localhost:5555 ./introducer
daemonize tahoe -d introducer run

Next, we attach a couple of storage nodes:

tahoe create-node --introducer $(cat introducer/private/introducer.furl) --nickname storage0 --webport 6001 --location tcp:localhost:6003 --port 6003 ./storage0
tahoe create-node --introducer $(cat introducer/private/introducer.furl) --nickname storage1 --webport 6101 --location tcp:localhost:6103 --port 6103 ./storage1
daemonize tahoe -d storage0 run
daemonize tahoe -d storage1 run

We can now tell the Grid Manager about our new storage servers:

grid-manager --config ./gm0 add storage0 $(cat storage0/node.pubkey)
grid-manager --config ./gm0 add storage1 $(cat storage1/node.pubkey)

To produce a new certificate for each node, we do this:

grid-manager --config ./gm0 sign storage0 > ./storage0/gridmanager.cert
grid-manager --config ./gm0 sign storage1 > ./storage1/gridmanager.cert

Now, we want our storage servers to actually announce these certificates into the grid. We do this by adding some configuration (in tahoe.cfg):

[storage]
grid_management = true

[grid_manager_certificates]
default = gridmanager.cert

Add the above bit to each node’s tahoe.cfg and re-start the storage nodes. (Alternatively, use the tahoe add-grid-manager command).

Now try adding a new storage server storage2. This client can join the grid just fine, and announce itself to the Introducer as providing storage:

tahoe create-node --introducer $(cat introducer/private/introducer.furl) --nickname storage2 --webport 6301 --location tcp:localhost:6303 --port 6303 ./storage2
daemonize tahoe -d storage2 run

At this point any client will upload to any of these three storage-servers. Make a client “alice” and try!

tahoe create-client --introducer $(cat introducer/private/introducer.furl) --nickname alice --webport 6401 --shares-total=3 --shares-needed=2 --shares-happy=3 ./alice
daemonize tahoe -d alice run
tahoe -d alice put README.rst  # prints out a read-cap
find storage2/storage/shares  # confirm storage2 has a share

Now we want to make Alice only upload to the storage servers that the grid-manager has given certificates to (storage0 and storage1). We need the grid-manager’s public key to put in Alice’s configuration:

grid-manager --config ./gm0 public-identity

Put the key printed out above into Alice’s tahoe.cfg in section client:

[grid_managers]
example_name = pub-v0-vqimc4s5eflwajttsofisp5st566dbq36xnpp4siz57ufdavpvlq

Now, re-start the “alice” client. Since we made Alice’s parameters require 3 storage servers to be reachable (--happy=3), all their uploads should now fail (so tahoe put will fail) because they won’t use storage2 and thus can’t “achieve happiness”.

A proposal to expose more information about Grid Manager and certificate status in the Welcome page is discussed in https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3506