docs: how to collect data from self-signed gitlab
diff --git a/docs/UserManuals/ConfigUI/GitLab.md b/docs/UserManuals/ConfigUI/GitLab.md
index 482e470..70ba46f 100644
--- a/docs/UserManuals/ConfigUI/GitLab.md
+++ b/docs/UserManuals/ConfigUI/GitLab.md
@@ -49,3 +49,28 @@
### Step 4 - Setting Sync Frequency
You can choose how often you would like to sync your data in this step by selecting a sync frequency option or enter a cron code to specify your prefered schedule.
+
+
+## FAQ
+
+### How to collect data from Gitlab server with Self-Signed Certificate
+There are two symptoms would exhibit when trying to collect data from a private Gitlab server with a Self-Signed certificate:
+
+1. "Test Connection" report error, this can be solved by setting the environment variable `IN_SECURE_SKIP_VERIFY=true` for the `devlake` container
+2. "GitExtractor" fails to clone the repository due to certificate verification, sadly, both `gogit` and `git2go` that we are using don't seem to support insecure HTTPS at all.
+
+A better approach would be adding your root CA to the `devlake` container:
+
+1. Mount your `rootCA.crt` into the `devlake` container
+2. Add a `command` node to install the mounted certificate
+```
+ devlake:
+ image: apache/devlake:v...
+ ...
+ volumes:
+ ...
+ - /path/to/your/rootCA.crt:/usr/local/share/ca-certificates/rootCA.crt
+ command: [ "sh", "-c", "update-ca-certificates; lake" ]
+ ...
+```
+
