diff --git a/.pylintrc b/.pylintrc
index d425187..9b1489b 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -148,7 +148,8 @@ disable=print-statement,
         duplicate-code,
         no-else-return,
         consider-using-enumerate,
-        too-many-lines
+        too-many-lines,
+        consider-using-f-string
 
 # Enable the message, report, category or checker with the given id(s). You can
 # either give multiple identifier separated by comma (,) or put this option
diff --git a/Dockerfile b/Dockerfile
index dc72f3b..cd1a593 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,7 +1,7 @@
 # NOTE: Use the run-container.sh script to build and launch this container.
 
 # NOTE: Multi-stage builds require Docker >= 17.05.
-FROM centos:8 AS base
+FROM rockylinux:8 AS base
 
 # update packages and install requirements
 RUN dnf -y upgrade-minimal && \
diff --git a/asl_rulebook2/bin/prepare_pdf.py b/asl_rulebook2/bin/prepare_pdf.py
index b90617c..a9c9543 100755
--- a/asl_rulebook2/bin/prepare_pdf.py
+++ b/asl_rulebook2/bin/prepare_pdf.py
@@ -32,10 +32,10 @@ def prepare_pdf( pdf_file,
     """Prepare the MMP eASLRB PDF."""
 
     # load the targets
-    with open( targets_fname, "r" ) as fp:
+    with open( targets_fname, "r", encoding="utf-8" ) as fp:
         targets = json.load( fp )
     if vo_notes_fname:
-        with open( vo_notes_fname, "r" ) as fp:
+        with open( vo_notes_fname, "r", encoding="utf-8" ) as fp:
             vo_notes_targets = json.load( fp )
     else:
         vo_notes_targets = None
@@ -116,7 +116,7 @@ def prepare_pdf( pdf_file,
 
 def _run_subprocess( args, caption, relinq ):
     """Run an external process."""
-    proc = subprocess.Popen( args )
+    proc = subprocess.Popen( args ) #pylint: disable=consider-using-with
     try:
         pass_no = 0
         while True:
diff --git a/asl_rulebook2/extract/content.py b/asl_rulebook2/extract/content.py
index 2769bb2..228fd93 100755
--- a/asl_rulebook2/extract/content.py
+++ b/asl_rulebook2/extract/content.py
@@ -783,7 +783,7 @@ class ExtractContent( ExtractBase ):
                 jsonval(caption[1]), jsonval(caption[0])
             )
         chapters = []
-        for chapter in self._footnotes:
+        for chapter in self._footnotes: #pylint: disable=consider-using-dict-items
             footnotes = []
             for footnote in self._footnotes[chapter]:
                 footnotes.append( "{}: {{\n  \"captions\": {},\n  \"content\": {}\n}}".format(
diff --git a/asl_rulebook2/tests/test_extract.py b/asl_rulebook2/tests/test_extract.py
index e517152..7b647dc 100644
--- a/asl_rulebook2/tests/test_extract.py
+++ b/asl_rulebook2/tests/test_extract.py
@@ -32,7 +32,8 @@ def test_extract_index():
 
         # check the results
         fname = os.path.join( dname, "index.txt" )
-        assert open( fname, "r", encoding="utf-8" ).read() == buf
+        with open( fname, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == buf
 
     # run the test
     for_each_easlrb_version( do_test )
@@ -61,13 +62,17 @@ def test_extract_content():
 
         # check the results
         fname2 = os.path.join( dname, "targets.txt" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == targets_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == targets_buf
         fname2 = os.path.join( dname, "chapters.txt" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == chapters_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == chapters_buf
         fname2 = os.path.join( dname, "footnotes.txt" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == footnotes_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == footnotes_buf
         fname2 = os.path.join( dname, "vo-notes.txt" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == vo_notes_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == vo_notes_buf
 
     # run the test
     for_each_easlrb_version( do_test )
@@ -99,15 +104,20 @@ def test_extract_all():
 
         # check the results
         fname2 = os.path.join( dname, "index.json" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == index_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == index_buf
         fname2 = os.path.join( dname, "targets.json" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == targets_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == targets_buf
         fname2 = os.path.join( dname, "chapters.json" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == chapters_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == chapters_buf
         fname2 = os.path.join( dname, "footnotes.json" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == footnotes_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == footnotes_buf
         fname2 = os.path.join( dname, "vo-notes.json" )
-        assert open( fname2, "r", encoding="utf-8" ).read() == vo_notes_buf
+        with open( fname2, "r", encoding="utf-8" ) as fp:
+            assert fp.read() == vo_notes_buf
 
     # run the test
     for_each_easlrb_version( do_test )
diff --git a/asl_rulebook2/utils.py b/asl_rulebook2/utils.py
index d946605..3e82b08 100644
--- a/asl_rulebook2/utils.py
+++ b/asl_rulebook2/utils.py
@@ -30,7 +30,7 @@ class TempFile:
         else:
             encoding = "utf-8" if "b" not in self.mode else None
         assert self.temp_file is None
-        self.temp_file = tempfile.NamedTemporaryFile(
+        self.temp_file = tempfile.NamedTemporaryFile( #pylint: disable=consider-using-with
             mode = self.mode,
             encoding = encoding,
             suffix = self.extn,
diff --git a/asl_rulebook2/webapp/asop.py b/asl_rulebook2/webapp/asop.py
index cc4c9b1..71c7e98 100644
--- a/asl_rulebook2/webapp/asop.py
+++ b/asl_rulebook2/webapp/asop.py
@@ -129,5 +129,5 @@ def _render_template( fname ):
         "ASOP_BASE_URL": url_for( "get_asop_file", path="" ),
     }
     args.update( _asop.get( "template_args", {} ) )
-    with open( fname, "r" ) as fp:
+    with open( fname, "r", encoding="utf-8" ) as fp:
         return fname, render_template_string( fp.read(), **args )
diff --git a/asl_rulebook2/webapp/main.py b/asl_rulebook2/webapp/main.py
index b71bb7e..b1fb6d2 100644
--- a/asl_rulebook2/webapp/main.py
+++ b/asl_rulebook2/webapp/main.py
@@ -69,7 +69,7 @@ def get_control_tests():
             servicer = ControlTestsServicer( app )
             add_ControlTestsServicer_to_server( servicer, server )
             port_no = parse_int( get_port(), -1 ) # nb: have to get this again?!
-            if port_no <= 0:
+            if port_no <= 0: #pylint: disable=consider-using-max-builtin
                 # NOTE: Requesting port 0 tells grpc to use any free port, which is usually OK, unless
                 # we're running inside a Docker container, in which case it needs to be pre-defined,
                 # so that the port can be mapped to an external port when the container is started.
diff --git a/asl_rulebook2/webapp/prepare.py b/asl_rulebook2/webapp/prepare.py
index c5b61d7..ea372ce 100644
--- a/asl_rulebook2/webapp/prepare.py
+++ b/asl_rulebook2/webapp/prepare.py
@@ -169,9 +169,9 @@ def _do_prepare_data_files( args, download_url ):
     with zipfile.ZipFile( zip_data, "w", zipfile.ZIP_DEFLATED ) as zip_file:
         fname_stem = "ASL Rulebook"
         zip_file.writestr( fname_stem+".pdf", pdf_data )
-        for key in file_data:
+        for key, fdata in file_data.items():
             fname = "{}.{}".format( fname_stem, key )
-            zip_file.writestr( fname, file_data[key] )
+            zip_file.writestr( fname, fdata )
     zip_data = zip_data.getvalue()
 
     # notify the front-end that we're done
diff --git a/asl_rulebook2/webapp/rule_info.py b/asl_rulebook2/webapp/rule_info.py
index b320fe1..d39bbea 100644
--- a/asl_rulebook2/webapp/rule_info.py
+++ b/asl_rulebook2/webapp/rule_info.py
@@ -184,8 +184,8 @@ def init_errata( startup_msgs, logger ):
             logger.info( "- Loaded %s.", plural(len(sources),"source","sources") )
 
     # fixup all the errata entries with their real source
-    for ruleid in _errata:
-        for anno in _errata[ruleid]:
+    for ruleid, annos in _errata.items():
+        for anno in annos:
             if "source" in anno:
                 anno["source"] = sources.get( anno["source"], anno["source"] )
 
diff --git a/asl_rulebook2/webapp/run_server.py b/asl_rulebook2/webapp/run_server.py
index c9db334..261167e 100755
--- a/asl_rulebook2/webapp/run_server.py
+++ b/asl_rulebook2/webapp/run_server.py
@@ -77,7 +77,8 @@ def main( bind_addr, data_dir, force_init_delay, flask_debug ):
         def _start_server():
             time.sleep( force_init_delay )
             url = "http://{}:{}".format( flask_host, flask_port )
-            _ = urllib.request.urlopen( url )
+            with urllib.request.urlopen( url ) as fp:
+                _ = fp.read()
         threading.Thread( target=_start_server, daemon=True ).start()
 
     # run the server
diff --git a/asl_rulebook2/webapp/startup.py b/asl_rulebook2/webapp/startup.py
index 64191e8..f232e3f 100644
--- a/asl_rulebook2/webapp/startup.py
+++ b/asl_rulebook2/webapp/startup.py
@@ -80,9 +80,7 @@ def init_webapp():
     # NOTE: This is quite a slow process (~1 minute for a full data load), which is why we don't do it inline,
     # during the normal startup process. So, we start up using the original content, and if the user does
     # a search, that's what they will see, but we fix it up in the background, and the new content will
-    # eventually start to be returned as search results. We could do this process once, and save the results
-    # in a file, then reload everything at startup, which will obviously be much faster, but we then have to
-    # figure out when that file needs to be rebuolt :-/
+    # eventually start to be returned as search results.
     if app.config.get( "BLOCKING_STARTUP_TASKS" ):
         # NOTE: It's useful to do this synchronously when running the test suite, since if the tests
         # need the linkified ruleid's, they can't start until the fixup has finished (and if they don't
diff --git a/asl_rulebook2/webapp/tests/test_asop.py b/asl_rulebook2/webapp/tests/test_asop.py
index d428c26..924a286 100644
--- a/asl_rulebook2/webapp/tests/test_asop.py
+++ b/asl_rulebook2/webapp/tests/test_asop.py
@@ -20,7 +20,7 @@ def test_asop_nav( webdriver, webapp ):
 
     # load the ASOP
     fname = os.path.join( os.path.dirname(__file__), "fixtures/asop/asop/index.json" )
-    with open( fname, "r" ) as fp:
+    with open( fname, "r", encoding="utf-8" ) as fp:
         asop_index = json.load( fp )
 
     # check the nav
@@ -64,7 +64,7 @@ def test_asop_content( webdriver, webapp ):
         fname = os.path.join( base_dir, fname )
         if not os.path.isfile( fname ):
             return None
-        with open( fname, "r" ) as fp:
+        with open( fname, "r", encoding="utf-8" ) as fp:
             return json.load( fp ) if as_json else fp.read()
 
     # load the ASOP index
@@ -121,6 +121,8 @@ def test_asop_content( webdriver, webapp ):
             assert content[0:20] in expected_content
 
         # check each individual section
+        def check_title():
+            return find_child( "#asop .title" ).text == expected
         for section_no, nav_section in enumerate( nav[chapter_no]["sections"] ):
 
             # click on the section in the nav pane
@@ -130,7 +132,7 @@ def test_asop_content( webdriver, webapp ):
             expected = expected_sections[ section_no ][ "caption" ]
             if expected_chapter.get( "sniper_phase" ):
                 expected += "\u2020"
-            wait_for( 2, lambda: find_child("#asop .title").text == expected )
+            wait_for( 2, check_title )
 
             # check the preamble
             # NOTE: The preamble is part of the parent chapter, and so should remain unchanged.
diff --git a/asl_rulebook2/webapp/tests/test_content_sets.py b/asl_rulebook2/webapp/tests/test_content_sets.py
index d76a557..5858474 100644
--- a/asl_rulebook2/webapp/tests/test_content_sets.py
+++ b/asl_rulebook2/webapp/tests/test_content_sets.py
@@ -1,5 +1,7 @@
 """ Test how content sets are handled. """
 
+from selenium.webdriver.common.by import By
+
 from asl_rulebook2.webapp.tests.utils import init_webapp, select_tabbed_page, get_curr_target, \
     set_stored_msg_marker, get_last_error_msg, find_child, find_children, wait_for, has_class
 from asl_rulebook2.webapp.tests.test_search import do_search
@@ -144,7 +146,7 @@ def _select_chapter( chapter_elem ):
     find_child( ".title", chapter_elem ).click()
     wait_for( 2, lambda: find_child( ".entries", chapter_elem ).is_displayed() )
     # make sure all other chapters are collapsed
-    parent = chapter_elem.find_element_by_xpath( ".." )
+    parent = chapter_elem.find_element( By.XPATH, ".." )
     assert has_class( parent, "accordian" )
     for elem in find_children( ".accordian-pane", parent ):
         is_expanded = find_child( ".entries", elem ).is_displayed()
diff --git a/asl_rulebook2/webapp/tests/test_doc.py b/asl_rulebook2/webapp/tests/test_doc.py
index c78efd5..93dc812 100644
--- a/asl_rulebook2/webapp/tests/test_doc.py
+++ b/asl_rulebook2/webapp/tests/test_doc.py
@@ -19,8 +19,8 @@ def test_doc( webapp, webdriver ):
     def get_doc( path ):
         # get the specified documentation file
         url = "{}/{}".format( webapp.base_url, path )
-        resp = urllib.request.urlopen( url ).read()
-        return resp.decode( "utf-8" )
+        with urllib.request.urlopen( url ) as resp:
+            return resp.read().decode( "utf-8" )
 
     # test a valid documentation file
     resp = get_doc( "/doc/prepare.md" )
diff --git a/asl_rulebook2/webapp/tests/test_prepare.py b/asl_rulebook2/webapp/tests/test_prepare.py
index 7d685f0..fc4346a 100644
--- a/asl_rulebook2/webapp/tests/test_prepare.py
+++ b/asl_rulebook2/webapp/tests/test_prepare.py
@@ -88,7 +88,8 @@ def test_full_prepare( webapp, webdriver ):
             assert zip_file.getinfo( "ASL Rulebook.pdf" ).file_size > 40*1000
             for ftype in [ "index", "targets", "chapters", "footnotes" ]:
                 fname = os.path.join( dname, ftype+".json" )
-                expected = json.load( open( fname, "r" ) )
+                with open( fname, "r", encoding="utf-8" ) as fp:
+                    expected = json.load( fp )
                 fdata = zip_file.read( "ASL Rulebook.{}".format( ftype ) )
                 assert json.loads( fdata ) == expected
 
diff --git a/asl_rulebook2/webapp/tests/utils.py b/asl_rulebook2/webapp/tests/utils.py
index 52ec45c..fc40248 100644
--- a/asl_rulebook2/webapp/tests/utils.py
+++ b/asl_rulebook2/webapp/tests/utils.py
@@ -8,6 +8,7 @@ import re
 import uuid
 
 from selenium.webdriver.support.ui import WebDriverWait
+from selenium.webdriver.common.by import By
 from selenium.common.exceptions import NoSuchElementException, TimeoutException
 
 from asl_rulebook2.utils import strip_html
@@ -40,9 +41,9 @@ def init_webapp( webapp, webdriver, **options ):
     _wait_for_webapp()
 
     # make sure there were no errors or warnings
-    startup_msgs = json.load(
-        urllib.request.urlopen( webapp.url_for( "get_startup_msgs" ) )
-    )
+    url = webapp.url_for( "get_startup_msgs" )
+    with urllib.request.urlopen( url ) as resp:
+        startup_msgs = json.load( resp )
     errors = startup_msgs.pop( "error", [] )
     errors = [ e[0] for e in errors ]
     assert set( errors ) == set( expected_errors )
@@ -171,7 +172,7 @@ def find_child( sel, parent=None ):
     try:
         if parent is None:
             parent = _webdriver
-        return parent.find_element_by_css_selector( sel )
+        return parent.find_element( By.CSS_SELECTOR, sel )
     except NoSuchElementException:
         return None
 
@@ -180,7 +181,7 @@ def find_children( sel, parent=None ):
     try:
         if parent is None:
             parent = _webdriver
-        return parent.find_elements_by_css_selector( sel )
+        return parent.find_elements( By.CSS_SELECTOR, sel )
     except NoSuchElementException:
         return None
 
diff --git a/conftest.py b/conftest.py
index aab14af..7d7d6b1 100644
--- a/conftest.py
+++ b/conftest.py
@@ -156,8 +156,9 @@ def _make_webapp():
         def is_ready():
             """Try to connect to the webapp server."""
             try:
-                resp = urllib.request.urlopen( app.url_for( "ping" ) ).read()
-                assert resp == b"pong"
+                url = app.url_for( "ping" )
+                with urllib.request.urlopen( url ) as resp:
+                    assert resp.read() == b"pong"
                 return True
             except URLError:
                 return False
@@ -167,9 +168,9 @@ def _make_webapp():
 
     # set up control of the remote webapp server
     try:
-        resp = json.load(
-            urllib.request.urlopen( app.url_for( "get_control_tests" ) )
-        )
+        url = app.url_for( "get_control_tests" )
+        with urllib.request.urlopen( url ) as resp:
+            resp = json.load( resp )
     except urllib.error.HTTPError as ex:
         if ex.code == 404:
             raise RuntimeError( "Can't get the test control port - has remote test control been enabled?" ) from ex
diff --git a/requirements-dev.txt b/requirements-dev.txt
index 57c6be4..25e1749 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,6 +1,6 @@
-pytest==6.2.2
-selenium==3.141.0
-grpcio==1.36.1
-protobuf==3.15.6
-pylint==2.6.2
+pytest==7.0.1
+selenium==4.1.0
+grpcio==1.44.0
+protobuf==3.19.4
+pylint==2.12.2
 pytest-pylint==0.18.0
diff --git a/requirements.txt b/requirements.txt
index 705f3df..ca2fb00 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,12 +1,12 @@
 # python 3.8.7
 
-flask==1.1.2
+flask==2.0.3
 flask-socketio==5.1.1
 eventlet==0.33.0
-pyyaml==5.4.1
-lxml==4.6.2
+pyyaml==6.0
+lxml==4.8.0
 markdown==3.3.6
-click==7.1.2
+click==8.0.4
 
-pdfminer.six==20201018
-pikepdf==2.5.2
+pdfminer.six==20211012
+pikepdf==5.0.1
diff --git a/setup.py b/setup.py
index de14c10..adbbfae 100644
--- a/setup.py
+++ b/setup.py
@@ -16,11 +16,12 @@ def parse_requirements( fname ):
     """Parse a requirements file."""
     lines = []
     fname = os.path.join( os.path.dirname(__file__), fname )
-    for line in open(fname,"r"):
-        line = line.strip()
-        if line == "" or line.startswith("#"):
-            continue
-        lines.append( line )
+    with open( fname, "r", encoding="utf-8" ) as fp:
+        for line in fp:
+            line = line.strip()
+            if line == "" or line.startswith("#"):
+                continue
+            lines.append( line )
     return lines
 
 # ---------------------------------------------------------------------