Running the server

Typically, the ZEO server is run using the runzeo script that’s installed as part of a ZEO installation. The runzeo script accepts command line options, the most important of which is the -C (--configure) option. ZEO servers are best configured via configuration files. The runzeo script also accepts some command-line arguments for ad-hoc configurations, but there’s an easier way to run an ad-hoc server described below. For more on configuring a ZEO server see Server configuration below.

Server quick-start/ad-hoc operation

You can quickly start a ZEO server from a Python prompt:

import ZEO
address, stop = ZEO.server()

This runs a ZEO server on a dynamic address and using an in-memory storage.

We can then create a ZEO client connection using the address returned:

connection = ZEO.connection(address)

This is a ZODB connection for a database opened on a client storage instance created on the fly. This is a shorthand for:

db = ZEO.DB(address)
connection = db.open()

Which is a short-hand for:

client_storage = ZEO.client(address)

import ZODB
db = ZODB.db(client_storage)
connection = db.open()

If you exit the Python process, the storage exits as well, as it’s run in an in-process thread.

You shut down the server more cleanly by calling the stop function returned by the ZEO.server function.

To have data stored persistently, you can specify a file-storage path name using a path parameter. If you want blob support, you can specify a blob-file directory using the blob_dir directory.

You can also supply a port to listen on, full storage configuration and ZEO server configuration options to the ZEO.server function. See it’s documentation string for more information.

Server configuration

The script runzeo runs the ZEO server. The server can be configured using command-line arguments or a configuration file. This document only describes the configuration file. Run runzeo -h to see the list of command-line arguments.

The configuration file specifies the underlying storage the server uses, the address it binds to, and a few other optional parameters. An example is:

<zeo>
  address zeo.example.com:8090
</zeo>

<filestorage>
  path /var/tmp/Data.fs
</filestorage>

<eventlog>
  <logfile>
    path /var/tmp/zeo.log
    format %(asctime)s %(message)s
  </logfile>
</eventlog>

The format is similar to the Apache configuration format. Individual settings have a name, 1 or more spaces and a value, as in:

address zeo.example.com:8090

Settings are grouped into hierarchical sections.

The example above configures a server to use a file storage from /var/tmp/Data.fs. The server listens on port 8090 of zeo.example.com. The ZEO server writes its log file to /var/tmp/zeo.log and uses a custom format for each line. Assuming the example configuration it stored in zeo.config, you can run a server by typing:

runzeo -C zeo.config

A configuration file consists of a <zeo> section and a storage section, where the storage section can use any of the valid ZODB storage types. It may also contain an event log configuration. See ZODB documentation for information on configuring storages.

The zeo section must list the address. All the other keys are optional.

address

The address at which the server should listen. This can be in the form ‘host:port’ to signify a TCP/IP connection or a pathname string to signify a Unix domain socket connection (at least one ‘/’ is required). A hostname may be a DNS name or a dotted IP address. If the hostname is omitted, the platform’s default behavior is used when binding the listening socket (‘’ is passed to socket.bind() as the hostname portion of the address).

read-only

Flag indicating whether the server should operate in read-only mode. Defaults to false. Note that even if the server is operating in writable mode, individual storages may still be read-only. But if the server is in read-only mode, no write operations are allowed, even if the storages are writable. Note that pack() is considered a read-only operation.

invalidation-queue-size

The storage server keeps a queue of the objects modified by the last N transactions, where N == invalidation_queue_size. This queue is used to support client cache verification when a client disconnects for a short period of time.

invalidation-age

The maximum age of a client for which quick-verification invalidations will be provided by iterating over the served storage. This option should only be used if the served storage supports efficient iteration from a starting point near the end of the transaction history (e.g. end of file).

transaction-timeout

The maximum amount of time, in seconds, to wait for a transaction to commit after acquiring the storage lock, specified in seconds. If the transaction takes too long, the client connection will be closed and the transaction aborted.

This defaults to 30 seconds.

client-conflict-resolution

Flag indicating that clients should perform conflict resolution. This option defaults to false.

msgpack

Use msgpack to serialize and de-serialize ZEO protocol messages.

An advantage of using msgpack for ZEO communication is that it’s a tiny bit faster and a ZEO server can support Python 2 or Python 3 clients (but not both).

msgpack can also be enabled by setting the ZEO_MSGPACK environment to a non-empty string.

Server SSL configuration

A server can optionally support SSL. Do do so, include a ssl subsection of the ZEO section, as in:

<zeo>
  address zeo.example.com:8090
  <ssl>
    certificate server_certificate.pem
    key server_certificate_key.pem
  </ssl>
</zeo>

<filestorage>
  path /var/tmp/Data.fs
</filestorage>

<eventlog>
  <logfile>
    path /var/tmp/zeo.log
    format %(asctime)s %(message)s
  </logfile>
</eventlog>

The ssl section has settings:

certificate

The path to an SSL certificate file for the server. (required)

key

The path to the SSL key file for the server certificate (if not included in certificate file).

password-function

The dotted name if an importable function that, when imported, returns the password needed to unlock the key (if the key requires a password.)

authenticate

The path to a file or directory containing client certificates to authenticate. (See the cafile and capath parameters in the Python documentation for ssl.SSLContext.load_verify_locations.)

If this setting is used. then certificate authentication is used to authenticate clients. A client must be configured with one of the certificates supplied using this setting.

This option assumes that you’re using self-signed certificates.

Running the ZEO server as a daemon

In an operational setting, you will want to run the ZEO server as a daemon process that is restarted when it dies. runzeo makes no attempt to implement a well behaved daemon. It expects that functionality to be provided by a wrapper like zdaemon or supervisord.

Rotating log files

runzeo will re-initialize its logging subsystem when it receives a SIGUSR2 signal. If you are using the standard event logger, you should first rename the log file and then send the signal to the server. The server will continue writing to the renamed log file until it receives the signal. After it receives the signal, the server will create a new file with the old name and write to it.