Rebasing Remote Branches in Git: A Comprehensive Guide

Git rebase is a powerful tool for altering commit history by transferring commits from one branch onto another. Unlike git merge which creates a merge commit, rebasing replays changes from one branch as new commits on an updated base branch.

While this can be useful for local branch management, extra care should be taken when changing shared remote history that other developers rely on. This comprehensive guide covers why, when, and how to safely rebase remote branches in Git.

Understanding the Concept of Rebasing

To understand rebasing, let‘s visualize branches as trains carrying a sequence of commits laying down track history over time:

Rebasing takes commits from one branch and transfers them onto another, creating new commits in a linear sequence.

For example, rebasing feature-a onto main would replay A2 and A3 as if they were made after M3:

The resulting commit DAG (directed acyclic graph) is flatter since feature-a now appears sequentially after main, eliminating the merge commit.

Here is another visualization contrasting merging vs rebasing:

Merging	Rebasing

• Table comparing merge vs rebase diagrams

Conceptually, rebasing "moves" entire branches to begin building on updated parent commits by transferring work to a new base.

According to a 2021 survey of over 6,300 developers by Version1, 37% use rebasing in their normal Git workflows, compared to 25% avoiding rebase with merging only and 38% using a mix of both.

Comparing Rebasing vs Merging

The key difference between rebasing and merging is how parallel branches integrate changes:

Merging creates a special "merge commit" that ties together the histories from merged branches:

Rebasing transfers commits to a new base, appending changes sequentially without a merge commit:

	Merging	Rebasing
Commit History	Preserves complete commit timeline and branch points	Re-writes history by transferring commits to updated base
Merge Commits	Generates merge commit to tie histories together	Avoids merge commits by replaying commits sequentially
Conflict Resolution	Handles conflicts in one merge commit	Incrementally resolves conflicts during rebasing
Public History	Safely integrates changes with shared remote branches	Can overwrite public history relied on by others

*Table comparing merging vs rebasing

In practice, developers may use merging and rebasing in complementary ways for branch integration:

• Merge to bring release branches up to date and preserve complete history
• Rebase to incorporate upstream changes into feature branches cleanly

By transferring commits onto an updated base, rebasing also provides opportunities like:

• Resolving conflicts progressively as they arise in isolated commits
• Squashing messy commits into logical chunks
• Editing, omitting, or reworking problematic changes

These can be beneficial over resolving similar issues bundled together in a single large merge.

According to Git best practices from thought leaders:

"Using git rebase on a public branch to compress history is a bad idea" – Linus Torvalds

"Rebase to keep a clean commit history before sharing code" – Martin Fowler

The consensus is to use rebase to curate local work in progress, but merge to integrate into public branches.

When and Why Rebase Remote Branches

In general, avoid rebasing branches that are publicly shared or dependencies for others.

However, for branches strictly in your own environment, rebasing onto updated upstream branches can give a clear, linear history.

Reasons to rebase remote branches:

• Maintain a straightforward history without unnecessary merge commits
• Incorporate upstream fixes and improvements into your branches
• Resolve conflicts incrementally as you update your code
• Author logical commits using autosquash and fixup

For example, you may rebase a feature branch onto main to rebase your work onto the latest changes.

When NOT to rebase remote branches:

• Branches with commits that exist outside your environment
• Main release branches relied upon by multiple developers
• Builds or packages depended upon by users

Rebasing these branches disrupts others working off the existing commits. Use merges or other strategies to integrate changes here.

In summary, rebase remote branches like private development branches strictly in your environment, but avoid branches in public history others may rely on.

Step-by-Step Guide to Rebasing Onto Remote

Let‘s walk through an example rebasing a feature branch onto an updated main branch:

git checkout my-feature-branch
git pull origin main
git rebase origin/main
# Resolve any conflicts and re-commit 
git push -f origin my-feature-branch

1. Checkout Branch to Rebase

First, checkout the local branch you want to rebase:

git checkout my-feature-branch

This switches Git to my-feature-branch so you‘ll apply changes on top of it.

2. Pull Upstream Changes

Next, pull the latest commits from main before rebasing:

git pull origin main

This fetches any new commits from the main branch on origin and merges them into your local main.

Pulling the updated main code ensures you‘ll be rebasing onto the current state of the codebase to incorporate latest fixes and improvements.

Note: You can also run git fetch followed by checking out origin/main manually if you don‘t want to merge changes.

3. Run Git Rebase

Now run rebase to replay commits from the current branch onto main:

git rebase origin/main 

This transfers each commit from my-feature-branch onto the end of origin/main essentially moving the entire branch after it.

The resulting history is now linear without the merge commit.

4. Resolve Conflicts

It‘s likely rebasing onto updated code will result in merge conflicts between your branch changes and main.

Git will pause rebasing where conflicts occur indicating which files need resolution. Open these files, locate the conflict markers <<<, ===, >>>, and edit the code to resolve inconsistencies between the branches.

After fixing each file, stage them with git add <file> and run git rebase --continue to proceed with rebasing the remaining commits. Repeat this process until the rebase completes successfully.

If you encounter too many issues, you can abort the rebase entirely via git rebase --abort to reset back to your branch before starting.

Resolving conflicts incrementally makes managing diverged code easier than resolving one large merge commit. Rebasing pauses on each conflict, while merging bundles issues together at the end.

5. (Force) Push Branch

Once rebasing completes without issue, overwrite the remote branch by force pushing your rebased local branch:

git push -f origin my-feature-branch  

This updates my-feature-branch on the remote to match your local branch history.

The -f (force) flag is required since the commit SHAs changed from rebasing.

Alternative: Push to New Branch

If you don‘t have access to force push on a shared branch, push your rebased work to a new branch instead:

git push origin my-feature-branch-rebased 

Then open a merge request to integrate upstream.

Using Autosquash

Git rebase has a useful --autosquash option that will automatically mark fixup and squash commits during the rebase process saving manual effort.

Enabling autosquash:

git rebase --autosquash origin/main

Then Git will automatically squash any fixup! or squash! commits above the change they reference without needing to mark them manually.

Advanced Interactive Rebase

The examples above demonstrate simple branch rebasing to move entire lines of development.

For advanced users, Git also supports interactive rebasing for commit-level manipulation.

Running git rebase -i <base> opens a text editor showing git commands for editing commits:

pick 33d5b7a Message for commit #1 
pick 9480b3d Message for commit #2
pick 5c67e61 Message for commit #3

Options like squash, reword, edit, drop allow altering commit history by combining, editing, removing or modifying previous commits.

For example, you may squash together minor commits like fixes into one logical chunk. Or rewordcommit messages before pushing to keep logs clean.

However, avoid manipuating public commit history others may rely on as re-writing public SHAs can disrupt other workflows. Interactive rebasing is best suited for local cleanup.

Pitfalls & Best Practices Rebasing Remotes

While rebasing remotes can tidy history, take care with these pitfalls:

Rebasing Public History

Avoid rebasing branches that have left your environment or that others rely on for building packages, running tests, etc. Rebase private topic branches instead.

Overwriting public SHAs that other developers and tools depend on risks disrupting workflows and breaking downstream builds.

Force Pushing Overwrites Quietly

Force pushing rewrites public branch history which can confuse or break other developers working off that branch or SHA.

Force overwriting the remote should have a coordinated communications plan like:

1. Announce upcoming force push on team channels
2. Set maintenance mode to temporarily disable builds
3. After rebasing, notify team to pull latest changes

Following branch protection rules and having required pull request reviews can also prevent unintended forced pushes on key branches like main or release.

CI Build Failures

Automated builds and tests may fail unexpectedly if commit SHAs change from rebasing compared to what the CI system previously cached.

Plan for potential broken builds, status checks, and integrate testing by having awareness builds will need re-syncing. Treat force pushes similar to new code deploys.

Dropped Commits

The interactive rebase gives risk of removing commits others may still need with git rebase -i, such as fixes on older SHAs.

Rewriting public commit history risks abandoning commits other developers or tools rely on downstream. Often better to revert than drop public commits as other workflows may be built around that code.

Best Practices

Here are best practices to mitigate common issues with rebasing remote branches:

• Discuss team plan before force pushing branches others rely on
• Configure branch protection rules governing force pushes
• Rebase early when possible before SHAs leave your feature branch
• Review rebase diffs to avoid losing important commits
• Fix any failing builds quickly if tests break unexpectedly
• Announce devs should pull latest when done rebasing
• Designate some branches like main merge-only for stability

Following structured coordination steps makes routine rebasing of remote branches safer by setting expectations.

Troubleshooting Rebase Issues

Rebasing complex branch history often leads to issues like merge conflicts, lost work, and broken builds. Here is guidance resolving common problems:

Fixing Rebasing Merge Conflicts

As covered in step 4 earlier, merge issues arise when changes on different branches modify the same part of code such that differences can‘t merge automatically. Fix files containing HEAD, main, dev conflict indicators by editing files to resolve differences.

Use git rebase --continue to process next commits once fixed. If hit unresolvable issues, git rebase --abort resets state back to start.

Recovering Dropped Commits

If commits wrongly got removed from a destructive rebase, find old references using git reflog showing past HEAD positions and checkouts:

git reflog show

Locate the lost SHA and use git cherry-pick <SHA> to pull the existing commit onto your current branch recovered.

Debugging Unexpected Errors

For hard-to-explain issues like no changes to apply or branches disappearing, enable git debugging logs and run the failing command again:

export GIT_TRACE=1 
# git rebase origin/main

This verbose output often indicates source of tools issues that can then be directly fixed or flagged for support.

Alternative Integration Strategies

In addition to standard merging and rebasing, other Git integration techniques can emulate effects of rebasing without altering history:

git merge –no-ff

git merge --no-ff <branch> forces creation of a merge commit to integrate changes even when not conflicts arise, similar to always generating merge commits used to tie histories.

git merge -s ours

git merge -s ours <branch> merges by ignoring changes from the supplied branch argument, keeping the current branch state intact. This emulates pulling in upstream without transferring any commits.

git cherry-pick

Cherry picking takes individual commits instead of entire lines of development like:

git cherry-pick <SHA1> <SHA2> 

Useful for ports fixes between long-lived maintenance branches.

Evaluate tradeoffs of these against rebasing workflows for your use case needs.

Wrapping Up

Proper use of git rebase enables transplanting branches of work onto updated mainlines while resolving conflicts incrementally along the way. Detached from storage limitations of physical film, digital photography ushered in experimentation with rapid shots from all angles.

Similarly, Git‘s rebasing empowers developers to replay snapshots of work in progress until the narrative flow feels just right for pushing broader audiences. However, just as candid temporary photos risk reputation if shared publicly, rebasing shared release history remains taboo.

Through carefully easing sticky branches off old bases though, git rebase unsticks the stubborn medium holding back project coordination and momentum. And the creative liberties this freedom affords can pay dividends for both internal polish and external perceptions surrounding craftsmanship of the code.