diff --git a/knowledge base/ansible.md b/knowledge base/ansible.md
index 1811200..67b9c3d 100644
--- a/knowledge base/ansible.md	
+++ b/knowledge base/ansible.md	
@@ -7,6 +7,7 @@
    1. [Loops](#loops)
 1. [Roles](#roles)
    1. [Get roles](#get-roles)
+   1. [Assign roles](#assign-roles)
    1. [Role dependencies](#role-dependencies)
 1. [Output formatting](#output-formatting)
 1. [Create custom filter plugins](#create-custom-filter-plugins)
@@ -270,6 +271,23 @@ ansible-galaxy install 'git+https://github.com/namespace/role.git,commit-hash'
 ansible-galaxy install -r 'requirements.yml'
 ```
 
+### Assign roles
+
+In playbooks:
+
+```yaml
+---
+- hosts: all
+  roles:
+    - web_server
+    - geerlingguy.postgresql
+    - role: /custom/path/to/role
+      vars:
+        var1: value1
+      tags: example
+      message: some message
+```
+
 ### Role dependencies
 
 Set them up in `role/meta/main.yml`:
@@ -652,11 +670,13 @@ See [Integrate with AWS SSM].
 - [Merging two dictionaries by key in Ansible]
 - [Creating your own Ansible filter plugins]
 - [Why Ansible and Python fork break on macOS High Sierra+ and how to solve]
-- [Ansible: Set variable to file content]
+- [Ansible: set variable to file content]
 - [How can I hide skipped tasks output in Ansible]
+- [Ansible roles: basics, creating & using]
 
 <!--
-  References
+  Reference
+  ═╬═Time══
   -->
 
 <!-- Knowledge base -->
@@ -681,6 +701,7 @@ See [Integrate with AWS SSM].
 [slurp]: https://docs.ansible.com/ansible/latest/collections/ansible/builtin/slurp_module.html
 
 <!-- Others -->
+[ansible roles: basics, creating & using]: https://spacelift.io/blog/ansible-roles
 [ansible: set variable to file content]: https://stackoverflow.com/questions/24003880/ansible-set-variable-to-file-content
 [check if a list contains an item in ansible]: https://stackoverflow.com/questions/28080145/check-if-a-list-contains-an-item-in-ansible/28084746
 [creating your own ansible filter plugins]: https://www.dasblinkenlichten.com/creating-ansible-filter-plugins/
diff --git a/knowledge base/cloud computing/aws/ecr.md b/knowledge base/cloud computing/aws/ecr.md
index 47f03ac..e598348 100644
--- a/knowledge base/cloud computing/aws/ecr.md	
+++ b/knowledge base/cloud computing/aws/ecr.md	
@@ -2,6 +2,8 @@
 
 1. [TL;DR](#tldr)
 1. [Pull through cache feature](#pull-through-cache-feature)
+1. [Troubleshooting](#troubleshooting)
+   1. [Docker pull errors with `no basic auth credentials`](#docker-pull-errors-with-no-basic-auth-credentials)
 1. [Further readings](#further-readings)
    1. [Sources](#sources)
 
@@ -70,6 +72,18 @@ aws ecr describe-repositories --repository-names 'docker-tools/image-builder' \
 > **Note:** when requesting an image for the first time using the pull through cache, the ECR creates a new repository for that image.<br>
 > This might™ introduce a small latency and be cause of pull failures. Pulling that (not-yet)cached image from an interactive shell session worked flawlessly.
 
+## Troubleshooting
+
+### Docker pull errors with `no basic auth credentials`
+
+Refer <https://github.com/awslabs/amazon-ecr-credential-helper/issues/207>.
+
+Context: trying to pull an image on an EC2 instance that is using the amazon-ecr-credential-helper to login.
+
+1. Check the user's `~/.ecr/log/ecr-login.log` file to get detailed information.
+1. Check the user's `~/.docker/config.json` file has a correct PAT.
+1. Check the instance's role has permissions to pull images.
+
 ## Further readings
 
 - [Amazon Web Services]
@@ -82,10 +96,10 @@ aws ecr describe-repositories --repository-names 'docker-tools/image-builder' \
 - [CLI subcommand reference]
 
 <!--
-  References
+  Reference
+  ═╬═Time══
   -->
 
-<!-- In-article sections -->
 <!-- Knowledge base -->
 [amazon web services]: README.md
 [cli]: cli.md
@@ -95,5 +109,3 @@ aws ecr describe-repositories --repository-names 'docker-tools/image-builder' \
 [cli subcommand reference]: https://docs.aws.amazon.com/cli/latest/reference/ecr/
 [creating a lifecycle policy preview]: https://docs.aws.amazon.com/AmazonECR/latest/userguide/lpp_creation.html
 [using pull through cache rules]: https://docs.aws.amazon.com/AmazonECR/latest/userguide/pull-through-cache.html
-
-<!-- Others -->