custom_header_persistence.md

Custom Header Persistence

Solution 1

Example is based on True-Client-IP header, the same principles can apply to Cookie persistence. Akamai's True-Client-IP header is way to recognize actual Client IP for all traffic routed through Akamai regional servers. Akamai inserts this header in each request with a value of the original user's IP address. This header can be used to define persistence for real client with the same backend server.

Persistence can be easily done through REST/UI/CLI: https://avinetworks.com/docs/17.2/custom-http-header-persistence/ or through Custom Datascript below:

Apply these scripts to the "HTTP REQUEST" & "HTTP RESPONSE" events appropriately ,pool has to be selected for datascript.

-- HTTP_REQUEST
default_pool = "primary_pool"
header = "True-Client-IP"
avi.vs.reqvar.header_value =  avi.http.get_header(header)
-- if header provided
if avi.vs.reqvar.header_value then
  -- lookup server using value of provided header for existing mapping in persistence table
  avi.vs.reqvar.pinned_server_ip = avi.vs.table_lookup(avi.vs.reqvar.header_value)
  -- assumming VS port matches server port
  pinned_server_port = avi.vs.port()
  -- if server found in persistence table and it's up, use already pinned server, if not use default pool
  if avi.vs.reqvar.pinned_server_ip and avi.pool.get_server_status(default_pool, avi.vs.reqvar.pinned_server_ip, pinned_server_port) == 1 then
    avi.pool.select(default_pool, avi.vs.reqvar.pinned_server_ip)
  else
    avi.vs.table_remove(avi.vs.reqvar.header_value)
    avi.pool.select(default_pool)
  end
end

-- HTTP_RESPONSE
if avi.vs.reqvar.header_value then
  selected_server_ip = avi.pool.server_ip()
  if avi.vs.reqvar.pinned_server_ip then
    -- Update the expire time for a table entry for 20 minutes for active connection i.e. existing persistence entry
    avi.vs.table_refresh(avi.vs.reqvar.header_value,1200)
  else
    -- Create persistence entry for 20 minutes based on header value
    avi.vs.table_insert(avi.vs.reqvar.header_value, selected_server_ip,1200)
  end
end

Solution 2

Custom Header Persistence based on supplied headers with downgrade to IP persistence if 'header1' or 'header2' is not provided. The datascript is leveraging avi.pool.get_server_info(), function got introduced since 17.2.14, 18.1.5 releases.

-- HTTP_REQUEST
default_pool = "primary_pool"
header1 = avi.http.get_header('Token')
header2 = avi.http.get_header('Authorization')

if header1 then
  avi.vs.reqvar.persist_value = header1
elseif header2 then
  avi.vs.reqvar.persist_value = header2
end

-- if header provided
if avi.vs.reqvar.persist_value then
  -- lookup server using value of provided header for existing mapping in persistence table
  if avi.vs.table_lookup(avi.vs.reqvar.persist_value) then
  -- split out the ip and port inside the table created
    avi.vs.reqvar.pinned_server_ip, avi.vs.reqvar.pinned_server_port = string.match(avi.vs.table_lookup(avi.vs.reqvar.persist_value), "(%d+.%d+.%d+.%d+):(%d+)")
  -- if server found in persistence table and it's up, use already pinned server
    if avi.vs.reqvar.pinned_server_ip and avi.vs.reqvar.pinned_server_port and avi.pool.get_server_status(default_pool, avi.vs.reqvar.pinned_server_ip, tonumber(avi.vs.reqvar.pinned_server_port)) == 1 then
      avi.pool.select(default_pool, avi.vs.reqvar.pinned_server_ip, tonumber(avi.vs.reqvar.pinned_server_port))
    end
  end
else
  avi.pool.select(default_pool)
end

-- HTTP_RESPONSE
if avi.vs.reqvar.persist_value then
  if avi.vs.reqvar.pinned_server_ip and avi.vs.reqvar.pinned_server_port then
    -- Update the expire time for a table entry for 20 minutes for active connection i.e. existing persistence entry
    avi.vs.table_refresh(avi.vs.reqvar.persist_value, 7200)
  else
    selected_server_ip, selected_server_port = avi.pool.get_server_info()
    -- Create persistence entry for 20 minutes based on header value
    avi.vs.table_insert(avi.vs.reqvar.persist_value, selected_server_ip..":"..selected_server_port, 7200)
  end
end