diff --git a/assets/images/ctls.png b/assets/images/ctls.png
new file mode 100644
index 0000000..871d3ff
Binary files /dev/null and b/assets/images/ctls.png differ
diff --git a/categories/devops.md b/categories/devops.md
index cf3ea26..693eac2 100644
--- a/categories/devops.md
+++ b/categories/devops.md
@@ -337,3 +337,8 @@ terraform apply # Apply changes to cluster
 
 
 ## Security
+
+
+### Mutual TLS authentication
+
+![CTLS](https://raw.githubusercontent.com/wahyd4/knowledge-mind-mapping/master/assets/images/ctls.png)
diff --git a/categories/go.md b/categories/go.md
index 222179c..d112e12 100644
--- a/categories/go.md
+++ b/categories/go.md
@@ -395,6 +395,13 @@ func main() {
 	}
 }
 ```
+## Some interesting mistakes
+
+### Do not reuse HTTP request when retrying
+
+See more information: https://stackoverflow.com/questions/55385894/http-contentlength-99-with-body-length-0
+
+
 
 # Useful links
 * [Go best practice](https://github.com/golang/go/wiki/CodeReviewComments)