diff --git a/docker/extract_indexes.sh b/docker/extract_indexes.sh
index a5ee45c..2ccfd50 100644
--- a/docker/extract_indexes.sh
+++ b/docker/extract_indexes.sh
@@ -1,109 +1,121 @@
 #!/bin/bash
 
 # Copyright (C) 2021-2022 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 WORKDIR=${1-/work}
 FILE_IN=$WORKDIR/nexus-maven-repository-index.gz
 
 localtime=$(date +"%Y-%m-%d %H:%M:%S")
 echo "Docker Script started on $localtime."
 echo "# Checks.."
 
 echo "* Content of /opt:"
 ls -l /opt
 echo "* Content of $WORKDIR:"
 ls -l $WORKDIR
 
 echo "* Will read files from [$FILE_IN]."
 
 if [ ! -r "$FILE_IN" ]; then
+    exit_code=4
     echo "Cannot find file [$FILE_IN]."
-    echo "Need an index file to work on. Exiting 4."
-    exit 4
+    echo "Need an index file to work on. Exiting ${exit_code}."
+    exit $exit_code
 else
     echo "*   Found file [$FILE_IN]."
 fi
 
 indexer=$(find /opt/ -name "indexer-cli-*.jar")
 if [ "$indexer" = "" ]; then
-    echo "Cannot find indexer. Exiting 6."
-    exit 6
+    exit_code=6
+    echo "Cannot find indexer. Exiting ${exit_code}."
+    exit exit_code
 else
     echo "*   Found indexer [$indexer]."
 fi
 
 clue=$(find /opt/ -name "clue-*.jar")
 if [ "$clue" = "" ]; then
-    echo "Cannot find clue. Exiting 8."
-    exit 8
+    exit_code=8
+    echo "Cannot find clue. Exiting ${exit_code}."
+    exit $exit_code
 else
     echo "*   Found clue [$clue]."
 fi
 
 echo "* Java version:."
 java -version
 
 echo "#############################"
 if [ -d $WORKDIR/indexes ]; then
     echo "Found $WORKDIR/indexes, skipping index generation."
     du -sh $WORKDIR/indexes/
 else
     echo "Unpacking [$FILE_IN] to $WORKDIR/indexes"
     java --illegal-access=permit -jar $indexer \
          --unpack $FILE_IN \
          --destination $WORKDIR/indexes/ \
          --type full 2>&1 | grep -v WARNING
 fi
 
 localtime=$(date +"%Y-%m-%d %H:%M:%S")
 echo "Unpacking finished on $localtime."
 
 echo "#############################"
-if [ -d $WORKDIR/export ]; then
-    echo "Found $WORKDIR/export, skipping index export."
-    ls -lh $WORKDIR/export/
+EXPORT_DIR=$WORKDIR/export/
+TEMP_FLD=$(find $EXPORT_DIR -name "*.fld")
+TEMP_FLD_LOCK=$(find $EXPORT_DIR -name "*.lock")
+
+if [[ -f $TMP_FLD && -f $TEMP_FLD_LOCK ]]; then
+    exit_code=1
+    echo "Found exported file $TEMP_FLD. Another process is updating it. Stopping."
+    exit $exit_code
+elif [[ -f $TMP_FLD && ! -f $TEMP_FLD_LOCK ]]; then
+    echo "Found final exported file $TEMP_FLD, skipping index export."
+    ls -lh $EXPORT_DIR
 else
     echo "Exporting indexes $WORKDIR/indexes to $WORKDIR/export"
     java --illegal-access=permit -jar $clue \
          $WORKDIR/indexes/ \
-         export $WORKDIR/export/ text 2>&1 | grep -v WARNING
+         export $EXPORT_DIR text 2>&1 | grep -v WARNING
 fi
 
 localtime=$(date +"%Y-%m-%d %H:%M:%S")
 echo "Exporting finished on $localtime."
 
 echo "#############################"
 
 echo "Cleaning useless files."
 
 echo "Size before cleaning:"
 du -sh $WORKDIR/*
 
 # We might want or not to delete the indexes
 # Remember that when they're not present, everything
 # gets recomputed every run..
-#echo "* Removing indexes."
-#rm -rf $WORKDIR/indexes/
+# echo "* Removing indexes."
+# rm -rf $WORKDIR/indexes/
 
 # If files others than the .fld one are required, please comment
 # the following lines.
 echo "* Removing useless exports."
 echo "  Keeping only fld text extract."
-rm -f $WORKDIR/export/*.inf
-rm -f $WORKDIR/export/*.len
-rm -f $WORKDIR/export/*.pst
-rm -f $WORKDIR/export/*.si
-rm -f $WORKDIR/export/segments*
+rm -f $EXPORT_DIR/*.inf
+rm -f $EXPORT_DIR/*.len
+rm -f $EXPORT_DIR/*.pst
+rm -f $EXPORT_DIR/*.si
+rm -f $EXPORT_DIR/segments*
+rm -f $EXPORT_DIR/*.lock
 
 echo "  Size after cleaning:"
 du -sh $WORKDIR/*
 
 echo "* Make files modifiable by the end-user."
-chmod -R 777 $WORKDIR/export/
+chmod -R 777 $EXPORT_DIR
 chmod -R 777 $WORKDIR/indexes/
 
 localtime=$(date +"%Y-%m-%d %H:%M:%S")
 echo "Docker Script execution finished on $localtime."
diff --git a/docker/run_full_export.py b/docker/run_full_export.py
index c40fd24..751d5e8 100644
--- a/docker/run_full_export.py
+++ b/docker/run_full_export.py
@@ -1,170 +1,175 @@
 # Copyright (C) 2021-2022 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import logging
 import click
 import sys
 import datetime
 import glob
 import re
-from subprocess import check_call
+from subprocess import check_call, CalledProcessError
 from os import chdir, makedirs
 from os.path import getsize, isabs, isdir, isfile, join, basename
 from pathlib import Path
 from shutil import copy2
 from urllib.parse import urljoin
 
 import requests
 
 logger = logging.getLogger(__name__)
 
 
 MAVEN_INDEX_NAME = "nexus-maven-repository-index"
 MAVEN_INDEX_ARCHIVE = f"{MAVEN_INDEX_NAME}.gz"
 
 
 def _download_indexes(base_url: str, work_dir: str) -> None:
     """Download all required indexes from the .index/ directory
     of the specified instance.
 
     """
     if base_url.startswith('test://'):
         logger.info("(Testing) Fake downloading required indexes")
         return None
 
     logger.info("Downloading required indexes")
 
     index_url = urljoin(base_url, ".index/")
 
     properties_name = f"{MAVEN_INDEX_NAME}.properties"
     properties_file = join(work_dir, properties_name)
     properties_url = urljoin(index_url, properties_name)
 
     # Retrieve properties file.
     logger.info("  - Downloading %s.", properties_file)
     content = requests.get(properties_url).content.decode()
     open(properties_file, "w").write(content)
 
     diff_re = re.compile("^nexus.index.incremental-[0-9]+=([0-9]+)")
     for line in content.split("\n"):
         diff_group = diff_re.match(line)
         if diff_group is not None:
             ind_name = f"{MAVEN_INDEX_NAME}.{diff_group.group(1)}.gz"
             ind_path = join(work_dir, ind_name)
             ind_url = urljoin(index_url, ind_name)
             if isfile(ind_path):
                 logger.info(
                     "  - File %s exists, skipping download.", basename(ind_path)
                 )
             else:
                 logger.info(
                     "  - File %s doesn't exist. Downloading file from %s.",
                     basename(ind_path),
                     ind_url,
                 )
                 # Retrieve incremental gz file
                 contentb = requests.get(ind_url).content
                 open(ind_path, "wb").write(contentb)
 
     # Retrieve main index file.
     ind_path = join(work_dir, MAVEN_INDEX_ARCHIVE)
     ind_url = urljoin(index_url, MAVEN_INDEX_ARCHIVE)
     if isfile(ind_path):
         logger.info("  - File %s exists, skipping download.", basename(ind_path))
     else:
         logger.info(
             "  - File %s doesn't exist. Downloading file from %s",
             basename(ind_path),
             ind_url,
         )
 
         contentb = requests.get(ind_url).content
         open(ind_path, "wb").write(contentb)
 
 
 @click.command()
 @click.option(
     "--base-url",
     required=True,
     help=(
         "Base url of the maven repository instance. \n"
         "Example: https://repo.maven.apache.org/maven2/"
     ),
 )
 @click.option(
     "--work-dir",
     help="Absolute path to the temp directory.",
     default="/tmp/maven-index-exporter/",
 )
 @click.option(
     "--publish-dir",
     help="Absolute path to the final directory.",
     default="/tmp/maven-index-exporter/publish/",
 )
 def main(base_url, work_dir, publish_dir):
     now = datetime.datetime.now()
     logger.info("Script: run_full_export")
     logger.info("Timestamp: %s", now.strftime("%Y-%m-%d %H:%M:%S"))
     logger.info("* URL: %s", base_url)
     logger.info("* Working directory: %s", work_dir)
     logger.info("* Publish directory: %s", publish_dir)
 
     # Check work_dir and create it if needed.
     if isdir(work_dir):
         logger.info("Work_Dir %s exists. Reusing it.", work_dir)
     else:
         try:
             logger.info("Cannot find work_dir %s. Creating it.", work_dir)
             Path(work_dir).mkdir(parents=True, exist_ok=True)
         except OSError as error:
             logger.info("Could not create work_dir %s: %s.", work_dir, error)
 
     assert isdir(work_dir)
     assert isabs(work_dir)
 
     # Grab all the indexes
     # Only fetch the new ones, existing files won't be re-downloaded.
     _download_indexes(base_url, work_dir)
 
-    # Extract indexes into a .fld file
-    check_call(["/opt/extract_indexes.sh", work_dir])
+    try:
+        # Extract indexes into a .fld file to publish
+        # this can raise if something is badly wired or something goes wrong
+        check_call(["/opt/extract_indexes.sh", work_dir])
+    except CalledProcessError as e:
+        logger.error(e)
+        sys.exit(4)
 
     logger.info("Export directory has the following files:")
     export_dir = join(work_dir, "export")
     makedirs(export_dir, exist_ok=True)
     chdir(export_dir)
     fld_file = None
     regexp_fld = re.compile(r".*\.fld$")
     for file_ in glob.glob("*.*"):
         logger.info("  - %s size %s", file_, getsize(file_))
         if regexp_fld.match(file_):
             fld_file = file_
 
     # Now copy the results to the desired location: publish_dir.
     if fld_file and isfile(fld_file):
         logger.info("Found fld file: %s", fld_file)
     else:
         logger.info("Cannot find .fld file. Exiting")
         sys.exit(4)
 
     makedirs(publish_dir, exist_ok=True)
     publish_file = join(publish_dir, "export.fld")
     logger.info("Copying files to %s.", publish_file)
     try:
         copy2(fld_file, publish_file)
     except OSError as error:
         logger.info("Could not publish results in %s: %s.", publish_dir, error)
 
     now = datetime.datetime.now()
     logger.info("Script finished on %s", now.strftime("%Y-%m-%d %H:%M:%S"))
 
 
 ###############################################
 # Start execution
 ###############################################
 
 if __name__ == "__main__":
     logging.basicConfig(level=logging.INFO)
     main(auto_envvar_prefix='MVN_IDX_EXPORTER')