Echo is a highly available NFS rig for Amazon Web Services.

It uses Redis as a backing store to maintain a Sorted Set maintaining last accessed time for a given file.

There are 3 different 'modes' that echo-fs can be run in, corresponding to the 3 different entry points:

• Listen - echo_listener.py: listens for messages from SNS or SQS. Sets SortedSet score, or copies file from S3->Nas depending on message.
• Populate - echo_populate.py: starting from folder walks repo and updates SortedSet to record path and set score = last access time (atime).
• Scavenger - echo_scavenger.py: if diskspace below threshold get a % of items from SortedSet and delete corresponding file if older than threshold.

If you want to run Echo on a volume that already has files in it, i.e. that Echo hasn't been made aware of during normal operations, you can populate Echo's Redis with the echo-populate.py script.

The following example assumes that you are considering a volume called efs.

Create a Redis instance:

docker run -d --name echo-redis redis:latest

Build the Echo image:

docker build -t echo-fs .

Populate Echo with contents of volume /efs:

docker run -t -i --name echo-populate --rm \
  -e ECHO_REDIS_HOST="echo-redis" \
  -e ECHO_REDIS_PORT="6379" \
  -e ECHO_REDIS_DB="0" \
  -e ECHO_CACHE_ROOT="/efs" \
  --link echo-redis:echo-redis \
  -v /efs:/efs \
  echo-fs \
  python -u echo_populate.py

You can then see if that is working by running the Scavenger in isolation:

docker run -t -i --name echo-scavenger --rm \
  -e ECHO_REDIS_HOST="echo-redis" \
  -e ECHO_REDIS_PORT="6379" \
  -e ECHO_REDIS_DB="0" \
  -e ECHO_CACHE_ROOT="/efs" \
  -e ECHO_SCAVENGER_CACHE_THRESHOLD="50" \
  -e ECHO_SCAVENGER_CHUNK_SIZE="2" \
  -e ECHO_SCAVENGER_SLEEP_SECONDS="1" \
  --link echo-redis:echo-redis \
  -v /efs:/efs \
  echo-fs \
  python -u echo_scavenger.py