HAProxy Enterprise Documentation 2.7r1

prepare map

Start a transaction made up of multiple map file changes.

Description

If you need to make multiple changes to a map file, and you need them to be applied all at the same time in one atomic change, submit them in a transaction using the prepare map and commit map commands.

  • Use prepare map to initiate the transaction.

  • Use add map and clear map as needed to make map changes.

  • Use show map to review the temporary version.

  • Use commit map to commit the changes and make them active in runtime memory.

The prepare map command starts the transaction by allocating a new version number for a map ID or filename returned by show map. The map ID or filename argument is passed to the prepare map command. The command responds with the new version number in the "New version created:" statement.

You can use the version number in the add map, clear map, and show map commands.

There is no impact of allocating new versions, as unused versions will automatically be removed once a more recent version is committed. Version numbers are unsigned 32-bit values which wrap at the end, so care must be taken when comparing them in an external program.

The prepare map operation creates an empty version of the map. Consequently, committing the version without first adding any entries effectively clears the map in runtime memory.

Examples

In this example, we start a new transaction for map file /etc/hapee-2.7/hosts.map.

$ echo "prepare map /etc/hapee-2.7/hosts.map" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock
New version created: 1

Contextual Example

This operation can be performed as part of a series of operations used to manage map files. The example in this section demonstrates how to modify mappings in HAProxy Enterprise's running configuration. The mappings are not persisted to the map file on disk. Any changes you make via the Runtime API are lost when the proxy halts.

Assume that you have a map file named /etc/hapee-2.7/routes.map with the following contents where the first column contains the keys and the second contains the values:

/cart/     cart_api
/reviews/  reviews_api

In the HAProxy Enterprise configuration, we reference this map file on a use_backend line with the map_beg fetch method. This tells the load balancer to choose the backend from the map file by matching the beginning of the requested URL path with a key in the file:

frontend fe_main
   bind :80
   use_backend %[path,map_beg(/etc/hapee-2.7/routes.map,be_servers)]

  1. Use the show maps command to list map files and their unique IDs. Here, the map file /etc/hapee-2.7/routes.map has an ID of 0:

    $ echo "show map" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock
    # id (file) description
0 (/etc/hapee-2.7/routes.map) pattern loaded from file '/etc/hapee-2.7/routes.map' used by map at file '/etc/hapee-2.7/hapee-lb.cfg' line 61. curr_ver=0 next_ver=1 entry_cnt=0

  2. Pass the map file's unique ID to show map to display entries in the file:

    $ echo "show map #0" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock
    0x563bbeeee160 /cart/ cart_api
0x563bbeeee1a0 /reviews/ reviews_api

  3. Pass the map file's unique ID to prepare map to start a transaction for map changes. Note the version number, which will be required in later commands. You can display version numbers using the show acl operation.

    $ echo "prepare map #0" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock
    New version created: 1

  4. Execute the set map command with these arguments: the map's ID, the key to be modified, and a new value to replace the key's existing value.

    Alternatively, use the map file's path instead of its ID.

    In the example below, we modify the /cart/ key, replacing the value cart_api with the value web_servers:

    $ echo "set map #0 /cart/ web_servers" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock

  5. Call commit map with the version and map ID to commit the change and make it active in runtime memory:

    $ echo "commit map @1 #0" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock

  6. Call show map to confirm the modification:

    $ echo "show map #0" | \
   sudo socat stdio unix-connect:/var/run/hapee-2.7/hapee-lb.sock
    0x563bbeeee160 /cart/ web_servers
0x563bbeeee1a0 /reviews/ reviews_api

See also

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