## ProFTPD module `mod_shaper`

The `mod_shaper` module is designed to split overall rates, both download and upload, for the `proftpd` daemon among all connected FTP clients, shaping each session to use only a portion of the overall rate. `mod_shaper` shapes both transmitted traffic, e.g. bits being downloaded via the `RETR` command, and received traffic, e.g. bits being uploaded via the `APPE`, `STOR`, and `STOU` commands.

This module is contained in the `mod_shaper.c` file for ProFTPD 1.2.x/1.3.x, and is not compiled by default. Installation instructions are discussed here. Detailed documentation on `mod_shaper` usage can be found here.

The most current version of `mod_shaper` is distributed with the ProFTPD source code.

## Author

Please contact TJ Saunders <tj at castaglia.org> with any questions, concerns, or suggestions regarding this module.

## Directives

- ShaperAll
- ShaperControlsACLs
- ShaperEngine
- ShaperLog
- ShaperSession
- ShaperTable

## Control Actions

- `shaper all`
- `shaper info`
- `shaper sess`

### ShaperAll

Syntax: ShaperAll ["priority" num] ["rate" num] ["downrate" num] ["uprate" num] ["shares" num] ["downshares" num] ["upshares" num]
Default: ShaperAll priority 10 rate -1.0 shares 5
Context: server config
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperAll` directive is used to configure the overall `mod_shaper` settings: the rate for the entire daemon, the default shares for shaped sessions, and the default priority for shaped sessions. If specified, the priority cannot be a negative number, the rates are in KB/s and must be greater than zero, and the shares must be greater than one. For configuring the priority and shares for individual sessions, use the `ShaperSession` directive.

The rate parameter sets both the downrate (i.e. download rate from the server) and the uprate (i.e. the upload rate to the server) at the same time. Use downrate and uprate if you wish to configure different rates for downloads and uploads. Similarly, the shares parameter sets both downshares and upshares.

The default rate is -1.0, which means that in order for `mod_shaper` to function properly, a rate, either rate, downrate or uprate, must be specified. The default shares setting is 5, the default priority is 10.

Examples:

      # Change the overall daemon rate to 100 KB/s
      ShaperAll rate 100

      # Give 20 shares to each session by default, and have an overall rate of 1000
      ShaperAll rate 1000 shares 20

      # Have a larger number of downshares than upshares
      ShaperAll rate 1000 downshares 2000 upshares 20

      # Configure separate download and upload rates
      ShaperAll downrate 1000 uprate 500

See also: `ShaperSession`

### ShaperControlsACLs

Syntax: ShaperControlsACLs actions|"all" "allow"|"deny" "user"|"group" list
Default: None
Context: server config
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperControlsACLs` directive configures access lists of users or groups who are allowed (or denied) the ability to use the actions implemented by `mod_shaper`. The default behavior is to deny everyone unless an ACL allowing access has been explicitly configured.

If "allow" is used, then list, a comma-delimited list of users or groups, can use the given actions; all others are denied. If "deny" is used, then the list of users or groups cannot use actions all others are allowed. Multiple `ShaperControlsACLs` directives may be used to configure ACLs for different control actions, and for both users and groups.

The actions provided by `mod_shaper` are "all", "info", and "sess".

Examples:

      # Allow only user root to alter the overall settings
      ShaperControlsACLs all allow user root

      # Allow the ftpadm group to shape current sessions
      ShaperControlsACLs sess allow group ftpadm

      # Allow everyone but user bob to see the current shaper stats
      ShaperControlsACLs info deny user bob

### ShaperEngine

Syntax: ShaperEngine on|off
Default: off
Context: server config, `<VirtualHost>`, `<Global>`
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperEngine` directive enables or disables the "shaping" of sessions by `mod_shaper`. If it is set to off this module does no shaping of transmitted traffic. Use this directive to disable the module instead of commenting out all `mod_shaper` directives.

### ShaperLog

Syntax: ShaperLog path|"none"
Default: None
Context: server config
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperLog` directive is used to specify a log file for `mod_shaper` reporting and debugging. The path parameter must be the full path to the file to use for logging. Note that this path must not be to a world-writeable directory and, unless `AllowLogSymlinks` is explicitly set to on (generally a bad idea), the path must not be a symbolic link.

If path is "none", no logging will be done at all.

### ShaperSession

Syntax: ShaperSession ["priority" num] ["shares" +|-num] ["downshares" +|-num] ["upshares" +|-num]
Default: ShaperSession priority 10
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperSession` directive is used to set shaping data on a per-session basis. It is intended to be used within `mod_ifsession` conditional configuration blocks. If used, the priority must not be a negative number. The shares parameters must start with '+' or '-'; these values adjust the default numbers of shares allotted to a session, increasing or reducing the sessions's shares. The `ShaperAll` directive is used for configuring overall shaping data.

The shares parameter sets both the downshares (i.e. shares of the download rate) and the upshares (i.e. shares of the upload rate) at the same time. Use downshares and upshares if you wish to configure different shares for downloads and uploads for the session.

Example:

      # Reward my friends
      ShaperSession shares +2

      # Punish my enemies
      ShaperSession shares -4

      # Allow for finer control over downloads by allocating more download
      # shares than upload shares for this session
      ShaperSession downshares +3 upshares -1

      # Let <Directory>-level TransferRate directives take priority
      ShaperSession priority 3

See also: `ShaperAll`

### ShaperTable

Syntax: ShaperTable path
Default: None
Context: server config
Module: mod_shaper
Compatibility: 1.2.10rc1 and later

The `ShaperTable` directive configures a path to a file that `mod_shaper` uses for storing its shaping data. The given path must be an absolute path. Note: this directive is required for `mod_shaper` to function.

## Control Actions

### `shaper all`

Syntax: ftpdctl shaper all [priority num] [rate num] [downrate num] [uprate num] [shares num] [downshares num] [upshares num]
Purpose: Alter overall mod_shaper settings

The `shaper all` action is used to change the overall `mod_shaper` settings on-the-fly. If specified, the priority cannot be a negative number, the rates are in KB/s and must be greater than zero, and the shares must be greater than one. For changing the priority and shares for individual sessions, use the `shaper sess` control action.

The rate parameter sets both the downrate (i.e. download rate from the server) and the uprate (i.e. the upload rate to the server) at the same time. Use downrate and uprate if you wish to configure different rates for downloads and uploads. Similarly, the shares parameter sets both downshares and upshares.

For example, to set the overall rate for the entire daemon to be 2000 KB/s:

      ftpdctl shaper all rate 2000

To give every session 10 shares, both downshares and upshares, by default:

      ftpdctl shaper all shares 10

To set the default priority for sessions:

      ftpdctl shaper all priority 3

Note that multiple parameters can also be used simultaneously:

      ftpdctl shaper all rate 2000 shares 10 priority 3

See also: `shaper sess`

### `shaper info`

Syntax: ftpdctl shaper info
Purpose: Print information about current shaped sessions

The `shaper info` control action can be used to view information on currently shaped sessions. This includes the current overall rate, the default number of shares per session, and the total number of currently shaped sessions. It also lists the following for each shaped session: process ID (PID), priority, downshare ("D") and upshare ("U") adjustments, and session downrate and uprate.

Example listing:

      # ftpdctl shaper info
      ftpdctl: Overall Rates: 1000.00 KB/s down, 500.00 KB/s up
      ftpdctl: Default Shares Per Session: 10 down, 10 up
      ftpdctl: Default Priority: 2
      ftpdctl: Number of Shaped Sessions: 2
      ftpdctl: PID   Priority DShares        DRate (KB/s) UShares        URate (KB/s)
      ftpdctl: ----- -------- -------------- ------------ -------------- ------------
      ftpdctl: 21750        2     12/24 (+2)       500.00      7/14 (-3)       250.00
      ftpdctl: 21753        2     12/24 (+2)       500.00      7/14 (-3)       250.00

The "DShares" and "UShares" columns are formatted as:

      sharessession/sharestotal (+|-sharesadjust)

The `+2` and `-3` in the listing above is due to a `ShaperSession` affecting these sessions:

      ShaperSession downshares +2 upshares -3

### `shaper sess`

Syntax: ftpdctl shaper sess class|host|user name [priority num] [shares +|-num]
Purpose: Alter specific session's mod_shaper settings

The `shaper sess` action is used to change session-specific shaping data on-the-fly. If given, the priority must not be a negative number. The shares parameters must start with '+' or '-'; these values adjust the default numbers of shares allotted to a session, increasing or reducing the sessions's shares.

The shares parameter sets both the downshares (i.e. shares of the download rate) and the upshares (i.e. shares of the upload rate) at the same time. Use downshares and upshares if you wish to configure different shares for downloads and uploads for the session.

This example gives user `alex` an additional 10 shares:

      ftpdctl shaper sess user alex shares +10

The following sets the priority for host `cache.example.com` such that `TransferRate` directives in `<Anonymous>` sections, `<Directory>` sections and `.ftpacccess` files have precedence (see the usage instructions for more details on priority):

      ftpdctl shaper sess host cache.example.com priority 2

One can even change the settings on entire Classes of sessions:

      ftpdctl shaper sess class proxy downshares -3 priority 1

See also: `shaper all`

## Installation

The `mod_shaper` module is distributed with ProFTPD. Follow the usual steps for using third-party modules in ProFTPD, making sure to include the `--enable-ctrls` configure option, which `mod_shaper` requires:

      $ ./configure --enable-ctrls --with-modules=mod_shaper

To build `mod_shaper` as a DSO module:

      $ ./configure --enable-ctrls --enable-dso --with-shared=mod_shaper

Then follow the usual steps:

      $ make
      $ make install

Alternatively, if your `proftpd` was compiled with DSO support, you can use the `prxs` tool to build `mod_shaper` as a shared module:

      $ prxs -c -i -d mod_shaper.c

## Usage

The `ShaperTable` is used to hold overall rates, both download and upload, for the entire daemon, the default number of shares and the default priority for each session. Then there is a list of shaping data for each particular session. To determine the portion of the overall rate that a session gets, `mod_shaper` calculates the total number of shares, and divides the overall rate by the total number of shares, resulting in a rate-per-share value:

      ratetotal / sharestotal = rateshare

The rate for a session is then the rate-per-share multiplied by the number of shares for that session:

      rateshare * sharessession = ratesession

Whenever a session starts or ends, `mod_shaper` recalculates the total number of shares and each session's rate, thus always adjusting values for each session so that the total of the session transfer rates never exceeds the overall `mod_shaper` rate. This means that `mod_shaper` divides the overall rate among all sessions (unless exempted), not just those sessions that are currently transferring files. Only if all shaped sessions are transferring data simultaneously will the overall rates be reached. Note that this calculation is performed separately for downloads and for uploads; sessions can have different shares of the download and upload rates.

Also, the transfer rate is calculated at the start of each transfer; the core `proftpd` engine does not recalculate the rate during the data transfer. This means, for example, that if a session gets 100 KB/s and starts a transfer, then a second session begins and gets 50 KB/s, the first session's transfer will continue to get 100 KB/s, until that transfer ends. The next transfer started by the first session would then get 50 KB/s, just like the second session.

By default, `mod_shaper` allots 5 shares for every session. Increasing the default number of shares for a session (using the `ShaperAll` configuration directive or the `shaper all` control action) does not increase the rate used by every session. If every session has the same number of shares, then the overall rate is divided evenly among the sessions; a higher default shares value results in a smaller rate-per-share value.

What is the benefit of increasing the default shares setting, then? It allows for finer-grained tuning of shaped sessions, using the `ShaperSession` directive and the `shaper sess` control actions. An example: given an overall rate of 100 KB/s, a default shares of 1, and 4 sessions, the rate-per-share will be 25 KB/s (100 / 4 = 25), and since each session has 1 share, the download rate for each session is 25 KB/s. Now, what if you want to change these setting on-the-fly, allow one of the sessions a higher transfer rate, and reduce the transfer rate for another session? You could add another share to the session for user `dave`:

      ftpdctl sess user dave shares +1

After this, the rate-per-share is 20 KB/s. The session belonging to user `dave` now has 2 shares, which means it has a download rate of 40 KB/s; the other sessions now have download rates of 20 KB/s. What about reducing the rate for one of the other sessions, one belonging to user `anonymous`? One might think that:

      ftpdctl sess user ftp shares -1

would work. It will not. You cannot reduce the number of shares for a given session below 1. `mod_shaper` rules do not allow this. However, if the default shares setting was higher, like 5 or 10, then the administrator would have enough shares for reducing a session's rate. The more default shares, the smaller the rate-per-share value, and thus the finer control, by adding or removing smaller increments, the administrator has over the shaped sessions.

`mod_shaper` uses the same mechanism that the standard `proftpd` configuration directive, `TransferRate`, uses for controlling a session's download rate. Using the same mechanism, though, means that `mod_shaper` may interfere with any `TransferRate` directives in your `proftpd.conf`. Which takes priority, `mod_shaper` or `TransferRate`? This is handled by assigning a priority to each each shaped session. The priority for `TransferRate` directives depends on the configuration context in which the directive appears:

TransferRate Priority

Context | Priority
`<Global>` | 1
server config | 2
`<VirtualHost>` | 2
`<Anonymous>` | 3
`<Directory>` | 4
`.ftpaccess` | 5

The default priority assigned to `mod_shaper` sessions is 10. This means that `mod_shaper` takes precedence over `TransferRate`. However, if the site administrator needs `<Directory>`-level or `.ftpaccess`-level `TransferRate` directives to take priority, then the `ShaperSession` directive and `shaper sess` control action can be used to assign a priority to shaped sessions that is lower than that for `<Directory>` and `.ftpaccess`.

Configuring `mod_shaper`
Now that you know how the module works, it's time to see how to construct a `proftpd.conf` that enforces the desired shaper policy. Configuration directives that affect the shaping of sessions have control action equivalents, i.e. `ShaperAll` and `shaper all`, `ShaperSession` and `shaper sess`.

This example `mod_shaper` configuration uses the defaults and shapes all sessions:

      <IfModule mod_shaper.c>
        ShaperEngine on
        ShaperLog /var/log/ftpd/shaper.log
        ShaperTable /var/log/ftpd/shaper.tab

        # An overall rate (in KB/s) must be set.  This line explicitly
        # sets both the download and upload rates to be the same.
        ShaperAll downrate 1500 uprate 1500

        # Allow all system users to see shaper info
        ShaperControlsACLs info allow user *

        # Allow FTP admins to alter settings both overall and per-session
        ShaperControlsACLs all,sess allow group ftpadm
      </IfModule>

To exclude some user from having their sessions shaped by `mod_shaper`, use `mod_ifsession` for a configuration that adds the following:

      <IfModule mod_shaper.c>
        <IfUser lucky>
          ShaperEngine off
        </IfUser>
      </IfModule>

which says "If `mod_shaper` is present, and if the user logging in is named 'lucky', then disable `mod_shaper` for this session." Note that sessions that are not shaped by `mod_shaper` cannot be shaped once the user has logged in. Normal `TransferRate` directives will still apply to non-shaped sessions.

Similarly, you may wish to have a user that should have a greater portion of the overall download rate available to them:

      <IfModule mod_shaper.c>
        <IfUser lucky>
          ShaperSession downshares +5
        </IfUser>
      </IfModule>

This gives user `lucky` an additional 5 shares of the download rate, on top of the default number of shares for a session. Users can likewise have their default number of shares reduced, if necessary:

      <IfModule mod_shaper.c>
        <IfGroup anonftp>
          ShaperSession downshares -3
        </IfUser>
      </IfModule>

The control actions supported by `mod_shaper` can also be used, while the daemon and sessions are running, to set the desired shaping values.

© Copyright 2004-2017 TJ Saunders
All Rights Reserved