The following environment variables are required:

DB_DIRECTORY  - path to the database directory (if relative, to `run` script)
USERNAME      - the username the server will run as if using `run` script
ELECTRUMX     - path to the electrumx_server.py script (if relative,
                to `run` script)
DAEMON_URL    - the URL used to connect to the daemon.  Should be of the form
                    http://username:password@hostname:port/
                Alternatively you can specify DAEMON_USERNAME, DAEMON_PASSWORD,
                DAEMON_HOST and DAEMON_PORT.  DAEMON_PORT is optional and
                will default appropriately for COIN.

The other environment variables are all optional and will adopt
sensible defaults if not specified.

COIN          - see lib/coins.py, must be a coin NAME.  Defaults to Bitcoin.
NETWORK       - see lib/coins.py, must be a coin NET.  Defaults to mainnet.
DB_ENGINE     - database engine for the transaction database.  Default is
                leveldb.  Supported alternatives are rocksdb and lmdb.
                You will need to install the appropriate python packages.
                Not case sensitive.
REORG_LIMIT   - maximum number of blocks to be able to handle in a chain
                reorganisation.  ElectrumX retains some fairly compact
                undo information for this many blocks in levelDB.
                Default is 200.
HOST          - the host that the TCP and SSL servers will use.  Defaults to
                localhost.
TCP_PORT      - if set will serve Electrum TCP clients on that HOST:TCP_PORT
SSL_PORT      - if set will serve Electrum SSL clients on that HOST:SSL_PORT
                If set, SSL_CERTFILE and SSL_KEYFILE must be filesystem paths.
RPC_PORT      - Listen on this port for local RPC connections, defaults to
                8000.
BANNER_FILE   - a path to a banner file to serve to clients.  The banner file
                is re-read for each new client.
DONATION_ADDRESS  - server donation address.  Defaults to none.

If you want IRC connectivity to advertise your node:

IRC             - set to anything non-empty
IRC_NICK        - the nick to use when connecting to IRC.  The default is a
                  hash of REPORT_HOST.  Either way 'E_' will be prepended.
REPORT_HOST     - the host to advertise.  Defaults to HOST.
REPORT_SSL_PORT - the SSL port to advertise.  Defaults to SSL_PORT.
REPORT_TCP_PORT - the TCP port to advertise.  Defaults to TCP_PORT.

If synchronizing from the Genesis block your performance might change
by tweaking the following cache variables.  Cache size is only checked
roughly every minute, so the caches can grow beyond the specified
size.  Also the Python process is often quite a bit fatter than the
combined cache size, because of Python overhead and also because
leveldb consumes a lot of memory during UTXO flushing.  So I recommend
you set the sum of these to nothing over half your available physical
RAM:

HIST_MB   - amount of history cache, in MB, to retain before flushing to
            disk.  Default is 250; probably no benefit being much larger
            as history is append-only and not searched.

UTXO_MB   - amount of UTXO and history cache, in MB, to retain before
            flushing to disk.  Default is 1000.  This may be too large
            for small boxes or too small for machines with lots of RAM.
            Larger caches generally perform better as there is
            significant searching of the UTXO cache during indexing.
            However, I don't see much benefit in my tests pushing this
            too high, and in fact performance begins to fall.  My
            machine has 24GB RAM; the slow down is probably because of
            leveldb caching and Python GC effects.  However this may be
            very dependent on hardware and you may have different
            results.