I'm trying to run Boinc client using Docker and on a Raspberry Pi (RPi). Any ideas why it's failing?

I'm using example docker run command:
docker run -d \
--name boinc \
--net=host \
--pid=host \
-v /opt/appdata/boinc:/var/lib/boinc \
-e BOINC_GUI_RPC_PASSWORD="xyz" \
-e BOINC_CMD_LINE_OPTIONS="--allow_remote_gui_rpc" \
boinc/client:arm32v7

The docker container starts but then exits within 20 seconds or so. The below is in the logs:
14-Jan-2020 19:29:06 [---] cc_config.xml not found - using defaults
14-Jan-2020 19:29:06 [---] Starting BOINC client version 7.12.0 for arm-unknown-linux-gnueabihf
14-Jan-2020 19:29:06 [---] log flags: file_xfer, sched_ops, task
14-Jan-2020 19:29:06 [---] Libraries: libcurl/7.61.0 OpenSSL/1.1.1 zlib/1.2.11 libidn2/2.0.5 libpsl/0.20.2 (+libidn2/2.0.4) nghttp2/1.32.1 librtmp/2.3
14-Jan-2020 19:29:06 [---] Data directory: /var/lib/boinc
14-Jan-2020 19:29:06 [---] No usable GPUs found
14-Jan-2020 19:29:06 [---] [libc detection] gathered: 2.28, Ubuntu GLIBC 2.28-0ubuntu1
14-Jan-2020 19:29:06 [---] Host name: piDesktop
14-Jan-2020 19:29:06 [---] Processor: 4 ARM ARMv7 Processor rev 3 (v7l) [Impl 0x41 Arch 7 Variant 0x0 Part 0xd08 Rev 3]
14-Jan-2020 19:29:06 [---] Processor features: half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32
14-Jan-2020 19:29:06 [---] OS: Linux Ubuntu: Ubuntu 18.10 [4.19.75-v7l+|libc 2.28 (Ubuntu GLIBC 2.28-0ubuntu1)]
.....
14-Jan-2020 19:29:06 [---] Setting up project and slot directories
dir_open: Could not open directory 'slots' from '/var/lib/boinc'.
14-Jan-2020 19:29:06 [---] Checking active tasks
14-Jan-2020 19:29:06 [---] Setting up GUI RPC socket
14-Jan-2020 19:29:35 [---] GUI RPC bind to port 31416 failed: 98

I must say I have zero knowledge of Docker, so you may have to figure out for yourself how to get this done.

-e BOINC_GUI_RPC_PASSWORD="xyz" \
-e BOINC_CMD_LINE_OPTIONS="--allow_remote_gui_rpc" \

14-Jan-2020 19:29:35 [---] GUI RPC bind to port 31416 failed: 98

You are failing communication because of no permission.
Most of the boinccmd commands are of the form <code>boinccmd [--host hostname] [--passwd passwd] command</code>, so why not try to add at least the password into the commands you give.
Like <code>-e BOINC_CMD_LINE_OPTIONS="--passwd 'password'" \ "--allow_remote_gui_rpc" \</code>

---

Does Docker need to run with Virtualization (VT) enabled?
If so, the Pi doesn't have that.

instead you can run Boinc straight from the pi, without virtualization.

Just do:

sudo apt install boinc

if that doesn't work, try the guide here, his PPA release works well on the Pi:
https://launchpad.net/~costamagnagianfranco/+archive/ubuntu/boinc