SimRel/Simultaneous Release Cycle FAQ
This page is to document answers to frequently asked questions about Simultaneous Release cycle, process or build.
- 1 What is the Simultaneous Release cycle ?
- 2 Why was the release cycle changed ?
- 3 What are the streams to work on ?
- 4 As my project is part of the release train do I have to follow the exact cycle ?
- 5 When can I add, update and remove API ?
- 6 My project is part of the Simultaneous Release but is quite stable. Do I have to provide new features for each release ?
- 7 Where can I find the latest working (staging) version ?
- 8 Where can I find the latest stable release ?
- 9 Where could I find previous stable release ?
- 10 What is the naming pattern for the releases ?
- 11 What is the schedule for the next releases ?
- 12 How do we join the simultaneous release train
- 13 When can projects join the release train ?
- 14 When can projects leave the release train ?
- 15 What are the most important URLs
- 16 Where can the common repository be tested, before it is rolled out for a milestone or release?
- 17 What is the staging repository?
- 17.1 What is staging, for the current, most forward looking, yet-to-be-released stream?
- 17.2 What's the best way to test with the staging repository?
- 18 Once I update my .aggrcon file, how can I start a build?
- 19 A build failed message says it can not find xyz.feature.group, but I have nothing with "feature.group" in the name?
- 20 A build failed message says it can not find version 1.2.3.v9 but I can see 1.2.3.v9 on the file system?
- 21 How is a final build made "invisible" until release?
- 22 I see that xyz is being pulled into the repository, how can I see who is pulling it in?
- 23 What if we need a rebuild, past our deadline?
- 24 Common errors and what to do about them
- 24.1 Aggregation model is inconsistent
- 24.2 Invalid pack.gz file
- 24.3 Unable to load repository
- 24.4 Cannot complete the install because one or more required items could not be found
- 24.5 Cannot complete the install because of a conflicting dependency
- 24.6 A bundle comes from a different repository than what a project contributes
- 25 Additional Information
What is the Simultaneous Release cycle ?
The releases will occur every 13 weeks. It will follow the planning below:
- M1 Friday Week 3 : Milestone 1
- all the projects are expected to contribute their latest working version for a 1st alignment
- Staging repo is built 
- EPP packages are released for tests 
- M2 Friday Week 6: Milestone 2
- API breakages are in
- all the projects are expected to contribute their latest working version for a 2nd alignment
- Staging repo is built 
- EPP packages are released for tests 
- M3 Friday Week 9 : Milestone 3
- all the projects are expected to contribute their latest working version for a 3rd alignment
- Staging repo is built 
- EPP packages are released for tests 
- RC1 Friday Week 10 :
- API & Feature freeze
- Staging repo is built 
- EPP packages are released for tests 
- RC2 Friday Week 11 :
- Only fixes. It is assumed all code is done by the end of RC2
- Staging repo is built 
- EPP packages are released for tests 
- Quiet Week 12:
- If all goes well, no changes will occur this week
- If a blocker is found, this week allows for a final respin.
- GA Wednesday Week 13 :
- https://www.eclipse.org/downloads/eclipse-packages/ is updated with the latest EPP packages
- http://download.eclipse.org/releases/latest is updated to point to the new release’s update site.
The releases will occur near the middle of June, September, December and March each year.
Why was the release cycle changed ?
There were different motivations to update the release cadence from one year to every 13 weeks. The main ones are:
- Ease the update from one release to another for the end user
- Let developers provide new features faster to their users
- Simplify the maintenance by keeping only one stream for contributors
What are the streams to work on ?
There is only one master stream, it will be updated continuously. This means that there will be no more service releases after Photon.
As my project is part of the release train do I have to follow the exact cycle ?
Individual projects may have their own cycle releases at any time if they need to, but all participants in the Simultaneous Release, are expected to participate fully in the Simultaneous Release. Projects are expected to contribute a working version to each cycle, even if it is the same as the previous one. What new features are added or what bugs are fixed is up to each project to decide, but each project must, at least, continue to "fit in"; build, install and avoid conflicts.
Projects are free to have their own schedules as long as they meet the deliverables & deadlines.
When can I add, update and remove API ?
It is possible to add, update and remove API on any release. API breaks should be contributed no later than M3 and API & feature freeze must occur at RC1. Each project is responsible for its own API deprecation policy.
My project is part of the Simultaneous Release but is quite stable. Do I have to provide new features for each release ?
No, you just need to provide the same version as the previous one but ensure that it continues to “fit in”, your build is ok, and it works fine.
For example, should API be added to a project on which you depend, you must commit to updating your project so it can continue to be compiled, run, and installed along with the updated dependencies. For example, if Platform’s IJavaProject adds API to an abstract class, your implementation in webtools.jsf must also add those new methods.
Where can I find the latest working (staging) version ?
The latest working version is available on http://download.eclipse.org/staging/xxx/ where xxx = 2018-12, 2018-09, photon, oxygen, neon...
Where can I find the latest stable release ?
One repository will be used, which will be continuously updated after each release: http://download.eclipse.org/releases/latest/
This will be a moving target pointing to the latest stable release at any time.
Where could I find previous stable release ?
All the stable releases will be also kept available on specific URLs according to the following pattern: http://download.eclipse.org/releases/xxx/ where xxx = 2018-12, 2018-09, photon, oxygen, neon...
What is the naming pattern for the releases ?
The releases will be named following the pattern year.month: Eclipse IDE YYYY-MM.
For instance Eclipse IDE 2018-09, Eclipse IDE 2018-12, Eclipse IDE 2019-03, Eclipse IDE 2019-06…
Note that unlike past years, the name will no longer change annually with an alphabetically increasing name (Kepler, Luna, Mars, Neon, Oxygen, Photon) but will instead remain the singular name of the train.
What is the schedule for the next releases ?
After the release of Photon in June, we has switched to the new release cadence starting from the 25th of June 2018. Releases are quarterly, or about every 13 weeks.
|+0 Frid.||+1 Mon.||+2 Tues.||+3 Wed.||EPP Thur.||Available Fri.|
|2018-09 (“GA”)||quiet: 14/09||quiet: 17/09||quiet: 18/09||GA : 19/09||-||-|
|+0 Frid.||+1 Mon.||+2 Tues.||+3 Wed.||EPP Thur.||Available Fri.|
|2018-12 (“GA”)||quiet: 14/12||quiet: 17/12||quiet:18/12||GA : 19/12||-||-|
How do we join the simultaneous release train
Pretty much any project that wants to join the release train can and are encouraged to. Of course, it does sometimes take more work ... it is not just a matter of timing. But, often makes things much easier for your adopters and users. You should discuss with your mentors and PMC if you have any doubts or to make sure they agree its appropriate for your project.
For "how to join", see Simultaneous Release Requirements document.
How to decide if offset is +N category
It depends on who you depend on and who depends on you. The Eclipse Platform is +0, so nearly everyone else is +1, +2, or +3. For example, if you highly depended on "webtools" (which is +2) then you'd have to be a +3.
If no one else depends on you, in release train, then +3 would be a good choice. Everyone else is somewhere in between.
Of course, the lines are not always clear and pure ... such as part of emf is required at +0 but part of it is later at +1. In such cases, projects usually mark themselves as +1 and "work out the details", project-to-project, with those that need things at +0. Another example, part of a project such as WTP might depend on part of DTP and DTP might depend on part of WTP, but both need to be +2 to "fit in". In cases such, the projects might have to work out plans or agreements about having the sensitive, overlapping parts to be stable and finished early (in both API and version numbers) so neither has to build against the literal final delivery of the other.
Keep in mind, the +N category means the last possible time to drop (without notifying others). You are welcome and encouraged to have a "warm-up drop" a week or so earlier, with your "near final" bits, just to see if anything breaks or effects others, even though your final delivery may not be until +N.
When can projects join the release train ?
The period to join the simultaneous release is at the beginning of any cycle, four times a year. The project needs to declare its intention to join before the +0 (Friday) of the M1 release week. The "statement of intent" is still exactly the same as today: projects must formally announce their participation on the cross-projects-issues-dev mailing list.
Once a year, EMO will take care of organizing the “opt-in” process as it is today, so that all projects already in the train can declare their intention to continue. Those not opting to continue will be removed, but can be re-added should their intention change.
When can projects leave the release train ?
A project can declare its intention to leave at any moment in the cycle. If it does, it should inform depending projects in advance, so they can adjust accordingly.
What are the most important URLs
- SimRel, the wiki category page for the current Simultaneous Release stream.
Where can the common repository be tested, before it is rolled out for a milestone or release?
The best place is the "staging area", by adding http://download.eclipse.org/staging/<release_name> to your "available software sites" list, e.g.
Note: to get the best test, disable all other repositories in your list, or you might end up pulling something from some other repository, not staging. Be aware that moving a specific build to "staging" may happen only every few days (if you need something promoted more urgently, just ask on cross-project list).
What is the staging repository?
Conceptually, it is simply a place to hold a repository temporarily ... until the repository is promoted to a released location.
What is staging, for the current, most forward looking, yet-to-be-released stream?
Before the actual release, a common milestone aggregation build is moved from 'staging' to the 'releases' area. For example, once, for each final milestone, staging is moved to
What's the best way to test with the staging repository?
There are a couple of good tests to do, before a staging repository is released:
Test staging all by itself
Just add the staging repository to the available software sites, using preferences, and ... very important ... make sure all other sites are disabled. This then gives you the best view that everything in that one repository is correct, and all dependencies can indeed be found, and things show up in categories as expected.
After confirming the categories are as expected, usually the next test is just to install things, fresh, but often it is a good idea to test various update sceneries, to make sure things work as expected (for example, if you already have M1 installed, then once M2 is ready, test to be sure it updates to M2 as expected.
Test staging as a pseudo composite
After confirming staging repository is correct, its often useful to then also (re)enable the released repository. Then, on install dialog, you can select "all available sites" and this effectively simulates what the eventual, final composite repository will look like to end users. There are cases, especially during initial development, where invalid features will show up. For example, if a feature was removed, renamed, its version reduced, or its category changed from one milestone to the next, it might still show up in the composite, and that might interfere with correct installation (see bug 314165), if not merely be confusing to end users. If there is a serious problem due to the composite, please open a bug in cross-project component and we'll decide if the composite should be changed or reduced to allow for correct installation.
Test EPP Package updates
For a release, EPP packages are added to the common repository via composite, so its exact (final) location is transparent to end-users.
But before a release, similar to above, you can use a pseudo composite to test if an EPP Package updates as expected. You'd need to follow (or ask on) the epp-dev list to know details, but in addition to the above staging repo, you would add (and enable) EPP's staging repo, which would usually have a form similar to the following:
Why do we use composites anyway, if there are potential problems with them?
Two reasons. First, we use composites in order to be able to test early to make sure there are no bugs in p2, etc., that need to be fixed.
Secondly, someone may be using a previous milestone as a runtime target, and once we remove it, it will invalidate that target, so we do not want to force everyone to "move up" all at the the same time. Some developers may need a few weeks to transition to the latest code. To save space, we do not try and save all previous milestones, though. Our goal is to maintain about 3 milestones in the composite. For example, if we had M1, M2, and M3 in the composite, once RC1 came out, we'd only have M2, M3, and RC1. But the number can not be guaranteed. If there are serious problem with providing the composite we will reduce it to just two, or even to just one, to make sure the repository is usable for testing and continued development.
Once I update my .aggrcon file, how can I start a build?
You don't need to. The build will start automatically, once you check in a .aggrcon file. The build project is checked every 15 minutes to see if any changes, and if so an aggregation build will start. It takes approximately 2 hours to run.
But what if I really want to kick off the build myself?
If you can't wait 15 minutes, you can start the build your self. Anyone that has authorization to check in a build file, should have authority to manually start a build.
Plus, there are some cases where someone may need to kick off a build manually. For example, if a build fails due to network issues. Another common case is that a build may fail, even though the contribution file is correct, the repository it points to might have had an error. Once the repository is corrected, there's no automatic mechanism to detect that change, so after the repository is corrected, a new build has to be manually started (that, or the contribution file "touched" and then checked in again). To manually start a build, just click the "Schedule a Build" button at the build status control page.
You need to login (with your committer ID):
Then click the "Schedule a Build" buttton:
A build failed message says it can not find xyz.feature.group, but I have nothing with "feature.group" in the name?
The suffix ".feature.group" is added to feature names, to refer to the whole feature ... the feature files themselves, but also all its included bundles and features ... to help distinguish it from the literal feature files. So "xyz.feature.group" just means the "xyz feature", conceptually. See Eclipse Help for detailed information about metadata.
A build failed message says it can not find version 1.2.3.v9 but I can see 1.2.3.v9 on the file system?
The key file, the one that "drives" P2, is the content.jar/xml file. Be sure to check the version numbers there. If, inside it, the installable unit (often a feature) says version="1.2.3.v8", then P2 will look no further and conclude that the 'v9' feature it is looking for is not there. This is usually a sign your meta data needs to be re-generated to match the contents on the file system.
How is a final build made "invisible" until release?
Web download pages?
You can put the zips in their download directory, so those large items can replicate to mirrors, but don't use any HTML that would cause them to be displayed as links to an end user. True, if someone knew the exact URL they could still get it, but the idea is that the URL is not widely announced or visible, so even if a few download it, it is not hit by thousands of downloads. Then, on release day, you'd update the HTML pages to make the downloads visible to browsers and click-able by users.
Tip : you can hide some particular builds from download pages using the hidden.txt file in downloads directory ( see for example emft : http://dev.eclipse.org/viewcvs/viewvc.cgi/www/modeling/emft/downloads/hidden.txt?root=Eclipse_Website&view=log )
There is a few ways to accomplish this, depending on if you have composite or simple repositories, but they all involve promoting the "main" parts of the repository (the artifacts, usually "plugins" and "features" directory) to their final location so those meaty parts can be replicating to mirrors, but do not put the metadata (usually content.jar and artifacts.jar) to their final location until "release day". p2 doesn't "see" the artifacts, until it can read the metadata.
I see that xyz is being pulled into the repository, how can I see who is pulling it in?
There are times when someone may see an old, or inappropriate, bundle being "pulled in" to the aggregation build, and they want to find out how or why it is being included. While the full rules for how p2 decides something is required, or satisfies a requirement, is beyond the scope of this FAQ, there are two ways to get started narrowing it down. Just to have a concrete example, I will use the use-case provided by bug 357171 to show a specific case, where some old (unsigned) version of org.eclipse.emf.teneo.hibernate.libraries was being included.
The quick approximate check of where its coming from
Check the console log for a message about mirroring the problematic bundle, and then look back "up" in the log, to see what repository is being processed at that point.
For, our example, searching for 'org.eclipse.emf.teneo.hibernate.libraries' we find the following line:
[exec] - mirroring artifact osgi.bundle,org.eclipse.emf.teneo.hibernate.libraries,1.0.1.v200907090915
Then, looking back "up" in the log, we see the following repositories were being used to pull things from:
[exec] Mirroring meta-data from from file:///home/data/httpd/download.eclipse.org/modeling/emf/updates/interim [exec] - mirroring meta-data reference http://download.eclipse.org/modeling/mdt/updates/ [exec] - mirroring artifacts reference http://download.eclipse.org/modeling/mdt/updates/ [exec] - mirroring meta-data reference http://download.eclipse.org/modeling/emf/updates/ [exec] - mirroring artifacts reference http://download.eclipse.org/modeling/emf/updates/ [exec] - mirroring meta-data reference http://download.eclipse.org/modeling/emft/updates/ [exec] - mirroring artifacts reference http://download.eclipse.org/modeling/emft/updates/ [exec] Mirroring artifacts from from file:///home/data/httpd/download.eclipse.org/modeling/emf/updates/interim
In some cases, this might be sufficient to track down the problematic contributor.
The detailed, exact check on requirements
If the log doesn't help, the definitive source of "requirements" can be seen in the content.jar/xml. It can be tricky to "find" the content.jar/xml file, depending on composites repositories, if compressed or not, etc., but for our example, from a temporary maintenance repository, you can download it from
Once unzipped, you can search for your bundle, in our case. searching for 'org.eclipse.emf.teneo.hibernate.libraries'.
You'll certainly find the IU that defines the bundle
<unit id='org.eclipse.emf.teneo.hibernate.libraries' version='1.0.1.v200907090915' singleton='false'>
That IU, by itself, doesn't help narrow down who is requiring it. But, continue to search.
The easy case of "Require-Bundle"
If you find a match in a "requires" element, you can see what bundle "requires" your bundle. If found, those matches would start with "<required" element and include the name of the bundle. In these cases, there is some bundle that uses "Require-Bundle" and should be easy to resolve with who ever is doing that.
The harder case of "Import-Package"
If you find no direct "<required" match, then that means p2 is deciding your bundle "fits" the requirements due to the packages it provides (exports), and some other bundle (or bundles) "imports" those packages. If there are just a few, uniquely named packages provided by your mystery bundle, you can search the content.xml file for who "requires" those packages and figure out what to do from there.
The hardest case
But, our example does not have such a happy ending. The IU 'org.eclipse.emf.teneo.hibernate.libraries' provides 264 packages! Some of those are fairly distinctly named, but some are very common, and very commonly "imported" by other bundles. While I did not try, it would be hard to narrow down to just a few other bundles that might be requiring the many exported packages. I do not know the exact details, but p2 does have some heuristics where it will give extra weight to include a bundle that satisfies the most requirements -- so, any bundle that provides (exports) a huge number of common packages is in danger of getting included unintentionally by p2.
Back to the quick approximate findings
Another approach is to go back to those repositories implied in the "The quick approximate check" above.
Ideally, it would be possible to provide a more specific repository for the CBI aggregator so it only looks in more currently correct repositories. For example, (and, I emphasize 'example', since I am unsure of Modeling project's policies and procedures) a repository for "../emf/updates/indigo/" might be more appropriate for indigo contributions than a high level "../emf/updates/" repository. Or, as another example, perhaps "../emf/updates/interim" repository is actually incorrect for Indigo contributions. In that case, you could search the *.aggrcon files to see who is using or providing that repository and work out a better alternative.
A caution on how not to solve
For cases such as this, where some old, inappropriate bundle is being included, one solution, one might think, would be to surgically remove it from its original repository. This is almost never a good idea, since someone, somewhere, might be depending on it being there ... released repositories are forever, or, at least, are supposed to be ... so great care is needed in changing released repositories.
What if we need a rebuild, past our deadline?
Everyone knows plans are just plans, and occasionally exceptions are required. While we can't cover every exception (after all ... they are exceptions) there are the some general principles of deciding if an exception is required. The same ideas apply to milestones, release candidates, and releases, but the impact levels are higher the further along a cycle is. If possible, naturally, it is best to handle problems within your own project, say, by providing a patch feature or update to your own project's software repository, but in some cases, that's not possible ... this FAQ entry is about those cases.
Questions to ask yourself (and answer, in your request for an exception or rebuild)
Not necessarily an exhaustive list ... but, some common questions:
- Is the bug something that effects IP or similar "legal requirements" from the Eclipse Foundation?
- Is the bug something that prevents other projects from working correctly?
- Is the bug something that causes install, or update, to fail, or otherwise leave an installation in a bad, unfixable state?
- Is the bug something that can not be solved by a patch feature, applied by users or adopters after the release?
- Is the bug a regression, from previous release?
- Do other projects have to recompile, once a bug is fixed? For example, are constants changed? APIs? version numbers?
- Do other projects need to retest, once a bug is fixed? That is, is it something that could potentially effect others ... such as a change in timing or synchronization of some "notification" to listeners? Or something clearly "internal" to your own code?
- Do you have the support, approval, or review of your Project Lead and PMC? (Or, otherwise follow what ever your project's rampdown process is?)
- Does it affect an EPP Package? Or just the common repository?
Past our +n day, but before window closes?
If we are still within the "drop window" for a deadline, but you are past your particular +n day, simply post a note to cross-project list, with any relevant questions and answers from above list, the bug number, and then just do it. (No need for further approval or coordination.)
Keep in mind that spinning new builds past your deadline can result in a lot of work for downstream projects and consumers as they make last minute adjustment to your change. Projects are generally willing to accommodate these changes as much as they can, but please keep this in mind and only do it when absolutely necessary.
Past the drop window?
In this case, it is completely past the drop window, after EPP packages have been built. In this case, you still need to post to cross-project list, with bug number, and relevant questions and answers from above list, but now explicit review/permission from Planning Council is also required. Please follow the Planning Council Exception Process, but in cases of "tight timing", the Planning Council has authorized the Planning Council Chair (currently Mélanie Bats) to make the initial decision and allow others to review later or in parallel.
Common errors and what to do about them
There are some errors that occur during aggregation builds that are pretty common and asked about frequently so will list some here in this FAQ. Please add others, if you notice any missing, and/or improve the answers if any of these are incomplete or not helpful enough.
Aggregation model is inconsistent
The title is typically how the error message always begins, and then has several lines of hard to read notations, which are probably easy to read if you know EMF real well. :) There are two common reasons for this error, both are related to the fact that in some cases, the *.aggrcon file and the simrel.aggr file must *both* be updated.
An interesting twist of this problem is that when it occurs there is no "blame mail" sent out. The reasoning is that "since the model is bad it is hard to trust the email data from the model". Another good reason to use Gerrit, since then you know (pretty much) the error is yours, if this error occurs after your contribution. Otherwise, the overall Simultaneous Release Engineer must figure out the offending party -- which is pretty easy to do if they use the CBI Aggregator Editor.
- If the hard-to-read notations mention something about "missing proxy" then it is likely a "contact email" (or a feature id) was added to the projects aggrcon file, but was not added to the simrel.aggr file. It is easiest to use the CBI Aggregation editor (on the simrel.aggr file) to add/remove the feature or the contact and also add to a contribution or category.
- If the hard-to-read notations mention something about custom categories and features that "do not refer to each other" then similar to the above, someone tried to add a feature to a category, but changed only their aggrcon file and not the simrel.aggr file. The solution is the same, use the Editor!
In both cases above, after the change is made, but the simrel.aggr file and the project's aggrcon file should show "changed" and both should be committed together.
Invalid pack.gz file
The actual error message is not nearly so clear as the title of this section, but more often says something like the following (from bug 492904)
- org.eclipse.core.runtime.CoreException: Unable to unpack artifact osgi.bundle,org.apache.hadoop.zookeeper,3.3.3.v201105210832 in repository file:/home/hudson/genie.simrel/.hudson/jobs/simrel.neon.runaggregator.BUILD__CLEAN/workspace/aggregation/final/aggregate: Invalid content:org/apache/zookeeper/server/upgrade/UpgradeMain.class
- Caused by: org.eclipse.osgi.signedcontent.InvalidContentException: The file "org/apache/zookeeper/server/upgrade/UpgradeMain.class" in the jar "/home/hudson/genie.simrel/.hudson/jobs/simrel.neon.runaggregator.BUILD__CLEAN/workspace/tmp/signatureFile6913692817837489877.jar" has been tampered!
The problem is that the "pack.gz" file is invalid. For this example the bundle is probably something like "org.apache.zookeeper.server", but technically the error only mentions the package name, and the "temp location" of the jar file.
An interesting twist to this problem is that p2 itself will not complain if someone is simply "installing" the bundle, since if an error occurs with the "pack.gz" version of a bundle, p2 automatically falls back and uses the "jar" version of a bundle. The reason that it is considered a blocking error during aggregation is that most large repositories should be "perfectly correct". It is no big deal if one out of several thousand was wrong, but imagine if 25% of those thousands were "invalid pack.gz files". The end-user will end up wasting a lot of time doing updates, and the infrastructure bandwidth would be increased for no good reason.
There are 2 or 3 or 4 possible solutions.
- The jar may may be being "re-signed" during the project's build. Re-signing actually does work sometimes but seldom when "pack.gz" is involved. Hence, one solution is for the project to stop re-signing the bundle (which is difficult for some build system, but which is now automatic for most cases at Eclipse.org).
- Pack200 (that produces the pack.gz file) does not work for each and every possible piece of Java byte codes. It should, but it doesn't. So a few solutions here:
- The best (or easiest) is for the project to specify at build-time not to use pack200 with that particular bundle.
- Even better (but very difficult, and only worth if it is a very large bundle), is that pack200 has options to specify to do the "packing" slightly differently. For this example, as one use of the options, it might work to tell pack200 not to pack the "org/apache/zookeeper/server/upgrade/UpgradeMain.class". (BTW, I do not even know if that is possible with Tycho. :)
- Another "quick fix" solution is to run a post build step to remove that specific pack.gz file from the project's repository. This is not as simple as deleting the pack.gz file, since it is specified in the metadata files as "being available" but there are some simple p2 ant tasks that can be used to remove it correctly (as an example, see the example mentioned in bug 492904.
Unable to load repository
The title is typically how the error message always begins and then the error message names the repository. This is a frustrating error since sometimes a contribution will make it through "validation" perhaps even a "cached build" and then the "clean build" job will fail. This is because, it most cases, someone really did remove the repository specified in their aggrcon file before they updated their aggrcon file (or, perhaps they removed it, thinking they would quickly replace it with another repo at the same URL).
Typically, you just need to start over and trigger the validation job and let things run its course. It it happens twice in a row, best to open a bug or contact the offending party since they may not know the effect they are having or may not have a very good procedure for creating and updating their repositories. Projects are supposed to leave any old repositories around at least long enough for they themselves to get a good aggregation build before removing the old one. There are ways of doing this! And, yes, it usually does involve creating a new repository and then updating your aggrcon file.
Cannot complete the install because one or more required items could not be found
The title is typically how the error message always begins and then the error message gets pretty cryptic. But, hidden in the cryptic part it will be specific about what could not be found and what it is that requires it.
The solution typically involves several projects sorting out what changed versions and how others should specify their requirements. A typical "integration time" problem that is typically easy to solve once the right projects sort it out.
I partially wanted to mention this problem, because very occasionally someone will say, "but I can see bungle xyz with version l.m.n on the file system, why can't the aggregator find it". There reason is that it does not matter (too much) what is on the file system, what matters is what is in the content metadata or artifacts metadata. It is pretty rare these days, but occasionally something goes wrong and the content metadata says the repository has version "1.0.0" so it does not matter that version "2.0.0" is on the file system, the "contract" on the meta data is only for "1.0.0". This is typically a build or mirroring problem and the project that owns that repository must fix it.
Cannot complete the install because of a conflicting dependency
As above, the title is typically how the error message begins and then the error message gets pretty cryptic. And, again, hidden in the cryptic part it will be the specifics about what is conflicting. It is likely harder to read, though, just because it is longer and involves several threads of dependencies. These errors typically all boil down a "singleton" being required, and the installer (p2) knows that multiple versions can not be satisfied at runtime.
The solution typically involves several projects sorting out what changed versions and how others should specify their requirements. In other words, a fairly typical "integration time" problem that is typically easy to solve once the right projects sort it out. One caution, though. Occasionally this is solved by someone specifying "extra wide" dependency ranges so that it is closer to "any version of that singleton is required". This is often not ideal if one project provides one version from their own repository but then "picks up" another version from someone else's repository during the aggregation run (or, when a user installs from the Sim. Release repository). It is better, usually, if all "solutions" match, no matter where a feature or project is installed from.
A bundle comes from a different repository than what a project contributes
There is no consistent error message for this case. In fact, it is normal and "working as designed" that bundles can come from other repositories. Or, even, a more extreme case, "imported packages" can come from other bundles than what one contribution may have been expecting. The fundamental reason is that p2 (via the CBI aggregator) solves "all the constraints" pulling from "all the repositories" as though, conceptually, they were all one large request to "install everything" so anything -- from any repository -- is "fair game" if it meets the constraints. As said, most of the time this is normal and p2 (and the CBI aggregator) are working as designed. This is mentioned in this "trouble shooting" section, though, because occasionally it will cause an error of some sort and it is usually difficult to understand why a different bundle or package was installed. The error might be anything from the wrong version of the platform (or other Eclipse project) being pulled in to functional error from having the wrong version of a third-party package being pulled in.
The exact solution will depend on the exact error, but in general the solution takes two paths: one, for the producers of repositories, is to make sure the repositories used in the aggrcon files point to a specific set of bundles, intended only for the project contributing them, and only for the release that is being created -- if projects have "overlap" in including, say, parts of another Eclipse project, those contributing must coordinate well so they each have the same versions in their repositories; the second path is that the 'consumer' of the bundle or package must specify their 'version range constraints' as narrow as possible and still be appropriately wide. Most solutions will be fairly straightforward, once it is remembered that when a contribution is "pulled" for the Sim. Release repository, all the repositories from all the other contributions are considered "fair game" from which to satisfy the requirements of the contribution -- it is not only limited to that one repository mentioned in the aggrcon. Obviously, if every project contributed only bundles (and packages) from their own project's namespace, then the problems mentioned in this bullet item would not occur. Sometimes though, and for good reasons, several projects have the same, or similar, packages in each of their repositories -- third party packages being the most obvious case, but sometimes it makes sense for a project (let's say, the Platform) to include in their repository some core dependencies they have on other Eclipse projects (such as EMF and ECF).