I could simply:

#!/bin/sh -

cat /var/log/my.web.host-access-log | awk '{ print $1; }' | ...
[download]

or some such to feed the logs to a resolver. But I'm ideally looking for a way to process the log(s) (connections) in "real time". So that the logs have the correct access times. I can imagine filtering , or piping it.

<beancounting>You don't need cat in that pipe, just let awk read directly from the logfile.</beancounting>

Back on topic: Name resolving takes time, causes some extra load, and can fail. Hence web servers generally prefer not to resolve the remote address for performance reasons. However, you could simply log to a pipe instead of logging into a file. Apache comes with logresolve, which is intended to run offline, but you could also use it "live". It's a simple filter. It might be a little bit too simple-minded:

To minimize impact on your nameserver, logresolve has its very own internal hash-table cache. This means that each IP number will only be looked up the first time it is found in the log file.

In other words: logresolve completely ignores any TTLs and so your live log will contain nonsense after running for a while. It's not a bug, as logresolve is intended to run offline and only for a short time.

Have a look at the daemontools. At least multilog is usable, it takes care of reliably logging, including rotating log files. There is no IP resolving program in daemontools, but djb also published djbdns, a modular DNS resolver. It contains dnsfilter that should do quite exactly what you want: Resolve an IP address at line start to a host name. You should perhaps install a local cache on the webserver. That way, DNS requests are cached by djb's dnscache, dnsfilter reads most responses from the local cache, and so, DNS requests become a lot less expensive.

To recap: Install a local DNS cache. Then log to a pipe that writes into dnsfilter. dnsfilter then logs into multilog, which creates a nice set of log files.

Alexander