Swaptacular Web API reverse proxy

This project implements a load balancing HTTP reverse proxy, that forwards Swaptacular Web API requests to servers. It is intended to be used when several instances (shards) of Accounting Authority, Creditors Agent, or Debtors Agent Web API servers are deployed. The ultimate deliverable is a docker image, generated from the project's Dockerfile.

How it works

The reverse proxy extracts the creditor's and/or debtor's ID from the the incoming HTTP request, calculates a 32-bit sharding key (using a strictly defined algorithm), and then, based on the sharding key, decides to which server to forward the incoming request.

Configuration

The behavior of the running container can be tuned with environment variables. Here are the most important settings with some random example values:

# To configure a "Creditors Agent" proxy, the MIN_CREDITOR_ID and
# MAX_CREDITOR_ID environment variables must be set, indicating
# that the creditors agent will be responsible for creditor IDs
# between "$MIN_CREDITOR_ID" and "$MAX_CREDITOR_ID". The values
# can be formatted as decimal integers (negative decimal integers
# are allowed), or as hexadecimal non-negative integers (with
# the "0x" prefix).
MIN_CREDITOR_ID=4294967296
MAX_CREDITOR_ID=8589934591

# To configure a "Debtors Agent" proxy, the MIN_DEBTOR_ID and
# MAX_DEBTOR_ID environment variables must be set, indicating
# that the debtors agent will be responsible for debtor IDs
# between "$MIN_DEBTOR_ID" and "$MAX_DEBTOR_ID". The values can
# be formatted as decimal integers (negative decimal integers are
# allowed), or as hexadecimal non-negative integers (with
# the "0x" prefix).
MIN_DEBTOR_ID=0x100000000
MAX_DEBTOR_ID=0x1ffffffff

# To configure an "Accounting Authority" proxy, *none of the*
# MIN_CREDITOR_ID, MAX_CREDITOR_ID, MIN_DEBTOR_ID and
# MAX_DEBTOR_ID environment variables must be set.


# The proxy will listen for HTTP requests on
# port "$APIPROXY_PORT" (default 8080). The path "/healthz" can be
# used as a readyness/liveness probe, and if the server has started,
# it will always return an HTTP 200 status code.
APIPROXY_PORT=8080

# The full path to the configuration file. Each line in the
# configuration file should start with a route specifier,
# followed by at least one space, followed by a web server
# URL (only "http://" server URLs are supported). Route
# specifiers consist of zero or more 0s or 1s, separated by dots,
# ending with a hash symbol ("#"). An example configuration file:
#
# 0.# http://first-server:8001
# 1.# http://second-server:8001
#
# or, for a sigle server:
#
# # http://the-only-server
#
# Note that the APIPROXY_CONFIG_FILE environment variable *must*
# be set, and the route specifiers in the configuration file must
# cover all possible bit masks. For example, the following
# configuration file is invalid:
#
# 0.# http://some-server
#
# because it does not cover sharding keys starting with a
# binary "1".
#
# Note: If the configuration file changes, the change will will
# be detected by the API proxy, and the new configuration will be
# loaded and applied automatically.
APIPROXY_CONFIG_FILE=/etc/apiproxy.conf